Yea, Dirkules made a good point there.
Also, this might sound stupid, but did you ever edit him during those two years? Some times when you play with a player from the start you need to get the game to 'redo' his overall rating. The overall rating is a product of his individual ratings, and sometimes when using a roster patch, the overall rating won't be correct, so when you edit him (or trade him.. aha!), the game will re-calculate his overall value.
What I'm getting at is that he always was a circa 65-70 rated player when he was with you, just that you didn’t think he was because the overall rating hadn't been re-calculated.
That's not very likely at all though, but there's a 0,01% chance