It depends on the catcher, but I couldn't tell you how to differentiate them. The random features of the game also come into play. But, the different letter ratings have varying significance. I look at baseball reference to get the actual numbers, and that gives a reasonable guesstimate. Keep in mind that PA numbers are prorated for 162 games, but all other numbers are raw numbers. I always proportion them out to 162 games, and guess from there. It is always a guess, performance histories also help. Generally they get less PBs than you might expect, but not always. I use dead ball era Cs quite frequently, those that normalize hitting well. Even those that have the appearance of good PB and E ratings might not have done as well as you might expect, based on the ratings. Get out your shovel and dig, dig, dig!!!