Everyone's A game is relative. If you don't know a particular statistic that is relevant to the spot you're in than you may not be playing it optimally. I think when people reference their A game it's usually using all the information that they have and trying NOT to have spots where they are "missing" a relevant statistic. Whether you have a HUD and have exact stats or you're playing live and are using estimated stats it is all relative. You could also be referring to calculating bet sizing, pot
odds, continuing ranges, and so forth based on pot size / outs / bet size. You should be making note of spots where you do not know what the correct decision is so that you can go back later and see if there were some statistics that could have led you to the right decision in game. That way next time you are prepared.