As Just Blaze tells it:

“I always wanted to make [U Don’t Know] bigger and better, and make the drums hit harder, and the bass more in your face. I always say to myself, ‘I wish I got the opportunity to do that over.’

“We always used to say that M.O.P should have been on that record, even though we all like the original.

“… Jay didn’t even tell anybody. I guess he was trying to surprise us, but he walked into the studio one day and was like, ‘Yo, put this in.’ Put in the CD, and it was M.O.P rhyming on ‘U Don’t Know.’

“This was my opportunity to do it all over again. … I had gotten a lot better at time stretching and my mixing had gotten a lot better. So the end result was a dope followup to a classic record, without it being disrespectful to the original. They sound really good back-to-back."

Sampled from “I’m Not to Blame” by Bobby Byrd
http://www.youtube.com/watch?v=7XyS-a_Vmt8&feature=player_embedded#at=47