Two players on the same team (so, the same training budgets, coaches, etc). Both are 36 yo pitchers, and neither has been injured this season. Both have seen relatively similar usage rates during the season.

And, yet, Harold Mayne, who actually has a 78 makeup, has decline pretty drastically this season, while Vic Corsi, who has a 68 makeup, has barely lost any skills this season. The only explanation that occurs to me is Corsi had a major injury last season, and maybe that 'advanced' his decline for this season?

Just wondering what I'm missing here.

I've had similar questions in the past and have sent in tickets about it.  The response I've always gotten is that every player has their own unique development and regression patterns.  While make up and training have an effect, they are not the only determining factors in when and how a player will start declining.

Big injuries often cause a big ratings drop.

Posted by tufft on 12/13/2014 8:40:00 PM (view original):
Big injuries often cause a big ratings drop.

Right. But neither player has been injured this season. Corsi had a major injury the previous season. Did that "speed up" his normal age-related decline, meaning that now he isn't declining this season because he already experienced that decline last season? It seems unlikely, but it is possible, I guess.

zeustis' response is about as plainly worded and accurate of an answer as you are going to get.