I agree with the forget the number of the offender part. It's far harder to explain to a coach why you let his star quarterback get creamed than it is to say you didn't have time to get the number.
They will probably know who it was holding anyway.
I also start 12 - 13 yards back but usually just outside the end. It does take a little more to chase down the roll-out or scramble to the far side but it gives me an extra step or two to react if he rolls my way.