Well, I wouldn't worry about keeping track of accesory lifts quite like you do one of your primary lifts (DL, Squat, Bench, whatever) but you should have a general sense if you are getting stronger in your accessory lifts. For instance I have been working on P. Rows for a while and I got up to a hard fought 285x1. This morning I hit 255x5 without a ton of struggle. I would say that this indicates a fair increase in accessory performance, even though all things were not equal (not a 1RM, not the same weight).

I believe Jim Wendler (EFS) says something like this "I don't know what my last max was, but I know for damn sure it wasn't 255x5" And I think it is important to keep that kind of sense about your progress. You may not be able to dial in exactly where you were, but you should know it wasn't where you are.