diff -u b/core/lib/Drupal/Core/Field/Plugin/migrate/field/Email.php b/core/lib/Drupal/Core/Field/Plugin/migrate/field/Email.php
--- b/core/lib/Drupal/Core/Field/Plugin/migrate/field/Email.php
+++ b/core/lib/Drupal/Core/Field/Plugin/migrate/field/Email.php
@@ -40,14 +40,6 @@
   }
 
   /**
-   * @deprecated in Drupal 8.5.x, to be removed before Drupal 9.0.x. Use
-   * defineValueProcessPipeline() instead.
-   */
-  public function processFieldValues(MigrationInterface $migration, $field_name, $data) {
-    return $this->defineValueProcessPipeline($migration, $field_name, $data);
-  }
-
-  /**
    * {@inheritdoc}
    */
   public function defineValueProcessPipeline(MigrationInterface $migration, $field_name, $data) {
diff -u b/core/modules/datetime/tests/src/Unit/Plugin/migrate/field/DateFieldTest.php b/core/modules/datetime/tests/src/Unit/Plugin/migrate/field/DateFieldTest.php
--- b/core/modules/datetime/tests/src/Unit/Plugin/migrate/field/DateFieldTest.php
+++ b/core/modules/datetime/tests/src/Unit/Plugin/migrate/field/DateFieldTest.php
@@ -30,8 +30,16 @@
 
     $this->setExpectedException(MigrateException::class, "Field field_date of type 'timestamp' is an unknown date field type.");
     $this->plugin->defineValueProcessPipeline($this->migration, 'field_date', ['type' => 'timestamp']);
+  }
+
+  /**
+   * This calls the deprecated processFieldValues() method to test backwards
+   * compatibility.
+   */
+  public function testUnknownDateTypeBackwardsCompatibility() {
+    $this->migration = $this->prophesize('Drupal\migrate\Plugin\MigrationInterface')->reveal();
+    $this->plugin = new DateField([], '', []);
 
-    // Retain backwards compatibility testing.
     $this->setExpectedException(MigrateException::class, "Field field_date of type 'timestamp' is an unknown date field type.");
     $this->plugin->processFieldValues($this->migration, 'field_date', ['type' => 'timestamp']);
   }
diff -u b/core/modules/datetime/tests/src/Unit/Plugin/migrate/field/d6/DateFieldTest.php b/core/modules/datetime/tests/src/Unit/Plugin/migrate/field/d6/DateFieldTest.php
--- b/core/modules/datetime/tests/src/Unit/Plugin/migrate/field/d6/DateFieldTest.php
+++ b/core/modules/datetime/tests/src/Unit/Plugin/migrate/field/d6/DateFieldTest.php
@@ -31,6 +31,15 @@
 
     $this->setExpectedException(MigrateException::class, "Field field_date of type 'timestamp' is an unknown date field type.");
     $this->plugin->defineValueProcessPipeline($this->migration, 'field_date', ['type' => 'timestamp']);
+  }
+
+  /**
+   * This calls the deprecated processFieldValues() method to test backwards
+   * compatibility.
+   */
+  public function testUnknownDateTypeBackwardsCompatibility() {
+    $this->migration = $this->prophesize('Drupal\migrate\Plugin\MigrationInterface')->reveal();
+    $this->plugin = new DateField([], '', []);
 
     // Retain backwards compatibility testing.
     $this->setExpectedException(MigrateException::class, "Field field_date of type 'timestamp' is an unknown date field type.");
diff -u b/core/modules/file/src/Plugin/migrate/field/d7/ImageField.php b/core/modules/file/src/Plugin/migrate/field/d7/ImageField.php
--- b/core/modules/file/src/Plugin/migrate/field/d7/ImageField.php
+++ b/core/modules/file/src/Plugin/migrate/field/d7/ImageField.php
@@ -16,14 +16,6 @@
 class ImageField extends FieldPluginBase {
 
   /**
-   * @deprecated in Drupal 8.5.x, to be removed before Drupal 9.0.x. Use
-   * defineValueProcessPipeline() instead.
-   */
-  public function processFieldValues(MigrationInterface $migration, $field_name, $data) {
-    return $this->defineValueProcessPipeline($migration, $field_name, $data);
-  }
-
-  /**
    * {@inheritdoc}
    */
   public function defineValueProcessPipeline(MigrationInterface $migration, $field_name, $data) {
diff -u b/core/modules/link/src/Plugin/migrate/cckfield/d7/LinkField.php b/core/modules/link/src/Plugin/migrate/cckfield/d7/LinkField.php
--- b/core/modules/link/src/Plugin/migrate/cckfield/d7/LinkField.php
+++ b/core/modules/link/src/Plugin/migrate/cckfield/d7/LinkField.php
@@ -37,14 +37,6 @@
     return ['link_field' => 'link_default'];
   }
 
-  /**
-   * @deprecated in Drupal 8.5.x, to be removed before Drupal 9.0.x. Use
-   * alterFieldInstanceMigration() instead.
-   */
-  public function processFieldInstance(MigrationInterface $migration) {
-    $this->alterFieldInstanceMigration($migration);
-  }
-
   public function alterFieldInstanceMigration(MigrationInterface $migration) {
     $process = [
       'plugin' => 'static_map',
diff -u b/core/modules/link/src/Plugin/migrate/field/d6/LinkField.php b/core/modules/link/src/Plugin/migrate/field/d6/LinkField.php
--- b/core/modules/link/src/Plugin/migrate/field/d6/LinkField.php
+++ b/core/modules/link/src/Plugin/migrate/field/d6/LinkField.php
@@ -37,14 +37,6 @@
   }
 
   /**
-   * @deprecated in Drupal 8.5.x, to be removed before Drupal 9.0.x. Use
-   * defineValueProcessPipeline() instead.
-   */
-  public function processFieldValues(MigrationInterface $migration, $field_name, $data) {
-    return $this->defineValueProcessPipeline($migration, $field_name, $data);
-  }
-
-  /**
    * {@inheritdoc}
    */
   public function defineValueProcessPipeline(MigrationInterface $migration, $field_name, $data) {
diff -u b/core/modules/link/src/Plugin/migrate/field/d7/LinkField.php b/core/modules/link/src/Plugin/migrate/field/d7/LinkField.php
--- b/core/modules/link/src/Plugin/migrate/field/d7/LinkField.php
+++ b/core/modules/link/src/Plugin/migrate/field/d7/LinkField.php
@@ -31,13 +31,8 @@
   }
 
   /**
-   * @deprecated in Drupal 8.5.x, to be removed before Drupal 9.0.x. Use
-   * alterFieldInstanceMigration() instead.
+   * {@inheritdoc}
    */
-  public function processFieldInstance(MigrationInterface $migration) {
-    $this->alterFieldInstanceMigration($migration);
-  }
-
   public function alterFieldInstanceMigration(MigrationInterface $migration) {
     $process = [
       'plugin' => 'static_map',
diff -u b/core/modules/migrate_drupal/src/Plugin/migrate/field/FieldPluginBase.php b/core/modules/migrate_drupal/src/Plugin/migrate/field/FieldPluginBase.php
--- b/core/modules/migrate_drupal/src/Plugin/migrate/field/FieldPluginBase.php
+++ b/core/modules/migrate_drupal/src/Plugin/migrate/field/FieldPluginBase.php
@@ -20,38 +20,63 @@
 abstract class FieldPluginBase extends PluginBase implements MigrateFieldInterface {
 
   /**
+   * Alters the migration for field definitions.
+   *
    * @deprecated in Drupal 8.5.x, to be removed before Drupal 9.0.x. Use
    * alterFieldMigration() instead.
+   *
+   * @see ::alterFieldMigration()
    */
   public function processField(MigrationInterface $migration) {
+    @trigger_error( 'Deprecated in Drupal 8.5.x, to be removed before Drupal 9.0.x. Use
+   * alterFieldMigration() instead.', E_USER_DEPRECATED);
     $this->alterFieldMigration($migration);
   }
 
+  /**
+   * {@inheritdoc}
+   */
   public function alterFieldMigration(MigrationInterface $migration) {
     $process[0]['map'][$this->pluginId][$this->pluginId] = $this->pluginId;
     $migration->mergeProcessOfProperty('type', $process);
   }
 
   /**
+   * Alert field instance migration.
+   *
    * @deprecated in Drupal 8.5.x, to be removed before Drupal 9.0.x. Use
    * alterFieldInstanceMigration() instead.
+   *
+   * @see ::alterFieldInstanceMigration()
    */
   public function processFieldInstance(MigrationInterface $migration) {
+    @trigger_error( 'Deprecated in Drupal 8.5.x, to be removed before Drupal 9.0.x. Use
+   * alterFieldInstanceMigration() instead.', E_USER_DEPRECATED);
     $this->alterFieldInstanceMigration($migration);
   }
 
+  /**
+   * {@inheritdoc}
+   */
   public function alterFieldInstanceMigration(MigrationInterface $migration) {
     // Nothing to do by default with field instances.
   }
 
   /**
+   * Alter field widget migration.
+   *
    * @deprecated in Drupal 8.5.x, to be removed before Drupal 9.0.x. Use
    * alterFieldWidgetMigration() instead.
+   *
+   * @see ::alterFieldWidgetMigration()
    */
   public function processFieldWidget(MigrationInterface $migration) {
     $this->alterFieldWidgetMigration($migration);
   }
 
+  /**
+   * {@inheritdoc}
+   */
   public function alterFieldWidgetMigration(MigrationInterface $migration) {
     $process = [];
     foreach ($this->getFieldWidgetMap() as $source_widget => $destination_widget) {
@@ -92,16 +117,20 @@
   }
 
   /**
+   * Alter field formatter migration.
+   *
    * @deprecated in Drupal 8.5.x, to be removed before Drupal 9.0.x. Use
    * alterFieldFormatterMigration() instead.
+   *
+   * @see ::processFieldFormatter()
    */
   public function processFieldFormatter(MigrationInterface $migration) {
+    @trigger_error('in Drupal 8.5.x, to be removed before Drupal 9.0.x. Use alterFieldFormatterMigration() instead.', E_USER_DEPRECATED);
     $this->alterFieldFormatterMigration($migration);
   }
 
   public function alterFieldFormatterMigration(MigrationInterface $migration) {
     $process = [];
-
     // Some migrate field plugin IDs are prefixed with 'd6_' or 'd7_'. Since the
     // plugin ID is used in the static map as the module name, we have to remove
     // this prefix from the plugin ID.
@@ -113,10 +142,15 @@
   }
 
   /**
+   * Defines the process pipeline for field values.
+   *
    * @deprecated in Drupal 8.5.x, to be removed before Drupal 9.0.x. Use
    * defineValueProcessPipeline() instead.
+   *
+   * @see ::defineValueProcessPipeline()
    */
   public function processFieldValues(MigrationInterface $migration, $field_name, $data) {
+    @trigger_error('Deprecated in Drupal 8.5.x, to be removed before Drupal 9.0.x. Use defineValueProcessPipeline() instead.', E_USER_DEPRECATED);
     return $this->defineValueProcessPipeline($migration, $field_name, $data);
   }
 
diff -u b/core/modules/migrate_drupal/src/Plugin/migrate/field/NodeReference.php b/core/modules/migrate_drupal/src/Plugin/migrate/field/NodeReference.php
--- b/core/modules/migrate_drupal/src/Plugin/migrate/field/NodeReference.php
+++ b/core/modules/migrate_drupal/src/Plugin/migrate/field/NodeReference.php
@@ -18,14 +18,6 @@
 class NodeReference extends FieldPluginBase {
 
   /**
-   * @deprecated in Drupal 8.5.x, to be removed before Drupal 9.0.x. Use
-   * defineValueProcessPipeline() instead.
-   */
-  public function processFieldValues(MigrationInterface $migration, $field_name, $data) {
-    return $this->defineValueProcessPipeline($migration, $field_name, $data);
-  }
-
-  /**
    * {@inheritdoc}
    */
   public function defineValueProcessPipeline(MigrationInterface $migration, $field_name, $data) {
diff -u b/core/modules/migrate_drupal/src/Plugin/migrate/field/UserReference.php b/core/modules/migrate_drupal/src/Plugin/migrate/field/UserReference.php
--- b/core/modules/migrate_drupal/src/Plugin/migrate/field/UserReference.php
+++ b/core/modules/migrate_drupal/src/Plugin/migrate/field/UserReference.php
@@ -18,14 +18,6 @@
 class UserReference extends FieldPluginBase {
 
   /**
-   * @deprecated in Drupal 8.5.x, to be removed before Drupal 9.0.x. Use
-   * defineValueProcessPipeline() instead.
-   */
-  public function processFieldValues(MigrationInterface $migration, $field_name, $data) {
-    return $this->defineValueProcessPipeline($migration, $field_name, $data);
-  }
-
-  /**
    * {@inheritdoc}
    */
   public function defineValueProcessPipeline(MigrationInterface $migration, $field_name, $data) {
diff -u b/core/modules/taxonomy/src/Plugin/migrate/field/TaxonomyTermReference.php b/core/modules/taxonomy/src/Plugin/migrate/field/TaxonomyTermReference.php
--- b/core/modules/taxonomy/src/Plugin/migrate/field/TaxonomyTermReference.php
+++ b/core/modules/taxonomy/src/Plugin/migrate/field/TaxonomyTermReference.php
@@ -19,14 +19,6 @@
 class TaxonomyTermReference extends FieldPluginBase {
 
   /**
-   * @deprecated in Drupal 8.5.x, to be removed before Drupal 9.0.x. Use
-   * defineValueProcessPipeline() instead.
-   */
-  public function processFieldValues(MigrationInterface $migration, $field_name, $data) {
-    return $this->defineValueProcessPipeline($migration, $field_name, $data);
-  }
-
-  /**
    * {@inheritdoc}
    */
   public function defineValueProcessPipeline(MigrationInterface $migration, $field_name, $data) {