Spam/junk/bulk email addresses are not automatically stored in the Collected Addresses address book. What gets stored in Collected Addresses are email addresses from recipients you sent messages to, and which were not yet stored in any other address book. Email addresses from messages in Inbox are not automatically stored at all. You can manually do that if you choose to though.

Thanks for responding. That being the case, I can only imagine that the spam addresses I found in collected addresses must then have been collected from messages that were responded to automatically while in absentia with my afk/vacation/unavailablity message. These were not identified by the filter as spam prior to those replies being sent.