If I understand you correctly, this has always happened (or has since I've been playing). I've always assumed it's improvements made during the offseason, but you're right, it's never been 'accounted' for. Take (at random) my 3 QB's in Chapman - Hayes. Season is rolling over, they finished S63 with total ratings of 511/492/446. Without allowing for tiny 2 game increase, they started S64 on 523/497/453 so an off season increase of 12/5/7. I think that is pretty standard
Is that what you're getting at?