In the annual rep league here on Meta Stack Exchange, it shows that I've earned 9,876 rep this year, and 10,359 rep overall. (It's updated every day at 0:00 UTC, and I so far have earned 1 rep today, since an answer I downvoted a while ago was deleted.)
The difference between my total rep and the rep I earned this year is 483, which means 483 of the rep I've earned is rep I earned in 2017 or earlier. This amount normally never changes, though I can see some reasons why it might change, such as if rep is recalculated and something affects a rep event occurring in a previous year (e.g. a vote from last year was invalidated due to user deletion, a post I made at that time was deleted or undeleted, etc.)
This amount, 483, was a recent change; it used to be 461. Ordinarily, I'd chalk this up to a rep event from last year being recalculated, but I've gone through my full rep history and I can see nothing of the sort happening. On the other hand, on the same day that this number changed from 461 to 483, this post of mine was undeleted, recalculating my rep and giving me back 22 (which happens to equal 483-461). It therefore makes sense if that post was from a previous year. However, the post is from this year, so it doesn't make very much sense.
Is there a bug in the way yearly rep in the rep league is calculated, in that rep regained from an undeleted post made the same year is not re-added to the rep earned this year (while it is subtracted properly upon deletion)? Or is there some other event that occurred in the three weeks before 2018 that I had my account that caused this difference to change, that I'm not seeing, and the change being equal to that is just a coincidence?