Definitely has to do with trades/acquisitions/call-ups. But unfortunatley it doesn't look like ratings have any bearing. It seems like a new player with the same number gets it. Which really stinks. I know it may not bother some but losing my number will really bug me. I'm a 90 overall and was #5. Now I'm #8 because apparently Eduardo Escobar got called up from Triple-A.
I will say that I'm cool with that if it has to do with players already on the 40-man that come back up that had the number first. But if I'm a 90 overall and we acquire some junk bench player who jacks my number, that's not cool. Hopefully it doesn't happen like that.