This issue report may have two purposes. It could help site builders like me who are using Views-6.x-3.x-dev and unable to get view attachments for Year, Week and Day working. It may also indicate to the module maintainers that Calendar still has a bug in the way options like calendar_type are defined and ultimately exported via views.
So I followed the workflow I have successfully used in the past to create a new calendar view on a fresh install. I enabled the default calendar view and cloned it. However, when I went to the calendar page the links to the other calendar displays were missing. I retraced my steps and discovered that the calendar period (under Calendar Settings) was defaulting to Month for each of the view attachments. This is apparently because the cloning operation which I gather is an export/import operation was not exporting the calendar period (calendar_type in the code) because it wasn't defined properly. To resolve the issue I had to edit each calendar period and select the value appropriate for the attachment. [Moreover, I also had to do this for the Month view even though it looked on the face of it that its option was set correctly. But that was just the default value rendered in the view form - the option was evidently not actually stored properly in the database and so the link to the Month view wasn't output to the calendar page. So, I had to update the Month display attachment for completeness.]
It looks like the cause of this issue was raised previously , but was bounced to the Views issue queue and that's as far as it got. I looked through the commits to see if it has been resolved and couldn't see tags for calendar-6.x.2.4 or calendar-6.x.-2.x-dev indicating that it had. I tried to understand Earl's point about options_definition but the code in calendar_plugin_display_attachment.inc looked like it was following Views API correctly. Hopefully, someone who understands what's going on can take a look at this as I suspect it is causing grief to others besides me. My apologies if this is a non-issue or has been addressed in elsewhere in the queue.