@jean @manton It's interesting that this also works with Scheduling, which I think is a great way for it to work; I scheduled a new "Finished Reading" post for a few months into 2022 and Epilogue immediately picked it up to be included in the "Year In Books" post.
It would be ridiculously good if you could also update the "Year In Books" post when you do this to include the book you've added to the year via scheduling, whether manually with some code or a degree of automation. For example, when you add the new back-dated post a prompt appears with the message "Since you've added a book to that year, do you want to update your Year In Books Post?" and an accompanying button to take you to the edit screen of said post.
If instead the method changes for tracking, then I assume it would work more like Goodreads, et al. That would be a shame since the blog-centric approach is so good both in general and for Micro.blog specifically.