Only successfully Migrate-ing one Field Collection item instead of unlimited

Thank you for the wonderful migrate module. @mikeryan, I have read many of your helpful posts.

For my case, I am moving information from a relatively complexly interconnected Drupal 6 site to it's hand-built counterpart in Drupal 7. Migrate D2D is great but I could not get my use case to fit, so I am using good old Migrate. I have successfully used Migrate to migrate users, profiles (profile2), pages (articles?), and individual items of field collections. I will simplify my case as much as possible for this support request.

In my systems, each faculty user can have a profile called profile_faculty. The faculty profile had an unlimited multigroup in D6 with Degree Type (field_degree_type: text) and Degree Details (field_degree_details: text). The D7 is the same but in a field collection and both the multigroup and field collection are called field_degrees_held.

So a simplified example would be of the form:
profile_faculty:'23'
field_degrees_held
delta:0 degree_type:'BA' degree_details:'University of Somewhere, 2012'
delta:1 degree_type:'MA' degree_details:'Another Institution, 2013'

My Migrate class code will migrate either delta 0 or delta 1, but not both. I realize that my source query has to pull a record for each. It seems to do this. However, I am not doing something right with adding the field collection values so that they do not overwrite each other.

I have reviewed all the migrate / field collection documentation I could find, including the migrate and field collection code. Clearly, I don't understand it enough or I would probably have my answer.

There is something I am missing to create more than one item in a Field Collection. [I must be very dense because it looks like a lot of people have figured it out.] Any hints? Please.

Here is the field collection migration code I am using.

<?php

class degreeMigration extends GEOGProfileMigration {
  public function __construct($arguments) {
    parent::__construct($arguments);

        $this->description = t('Migration of degree multi-group info D6 to field collection D7');

        //specify dependencies.  Since this is a field collection, depends on the migration of the Profile (to which it is attached)
        //this is the name given to the Profile part of the "GEOGProfileMigration", so therefore it is "GEOGProfiles"
        $this->dependencies = array('GEOGProfiles');

        //create the query for the source data
        $query = db_select(OUR_SOURCE_DATABASE .'.node', 'n')
             ->fields('n', array('nid', 'type', 'language', 'title', 'uid', 'status', 'created', 'changed', 'comment', 'promote', 'moderate', 'sticky', 'tni$
              ->condition('n.type', 'profile_faculty', '=');

        $query->leftJoin(OUR_DEST_DATABASE .'.migrate_map_geogprofilesfcdegrees', 'map', 'map.sourceid1 = n.uid');

        $query->leftJoin(OUR_SOURCE_DATABASE .'.content_field_degree_details', 'dd', 'n.nid = dd.nid');
                $query->addField('dd', 'field_degree_details_value');
        $query->leftJoin(OUR_SOURCE_DATABASE .'.content_field_degree_type', 'dt', 'n.nid = dt.nid and dd.delta = dt.delta');
                $query->addField('dt', 'field_degree_type_value');
        $query->orderBy('n.uid','ASC');

        $this->source = new MigrateSourceSQL($query);

        //specify destination.   copied this from instructions on https://drupal.org/node/1900640
        $this->destination = new MigrateDestinationFieldCollection('field_degrees_held',
                                        array('host_entity_type' => 'profile2')  );

        $this->map = new MigrateSQLMap($this->machineName,
                array(
                        'uid' => array(
                                'type' => 'int',
                                'unsigned' => TRUE,
                                'not null' => TRUE,
                                'description' => 'D6 unique user ID',
                                'alias' => 'n',
                        ),
                ),
                MigrateDestinationFieldCollection::getKeySchema()
    );

        //map host entity ID to source entity ID
      $this->addFieldMapping('host_entity_id', 'uid')->sourceMigration('GEOGProfiles');

    $this->addFieldMapping('field_degree_type','field_degree_type_value');
    $this->addFieldMapping('field_degree_details','field_degree_details_value');
  }

}

?>

This is based on a class GEOGProfileMigration, which I can post as well, if that helps. It is pulling from the source database and the $this->map is as such:

<?php
 $this->map = new MigrateSQLMap($this->machineName,
      array(
        'uid' => array(
          'type' => 'int',
          'unsigned' => TRUE,
          'not null' => TRUE,
          'description' => 'D6 Unique User ID',
          'alias' => 'u',
        )
      ),
      MigrateDestinationProfile2::getKeySchema()
    );
?>

I have spent many, many hours/days/weeks trying to get this migration going - and wanted to try everything I could before bringing my noob question to the Drupal site. So please know that I am extremely grateful for any guidance.