I agree that a bat needs to be used for a while before you can judge its true performance but here is another thing. For someone like me who has gone through a lot of bats, enough every year that I could have started a small shop, you can tell early on too if a bat if going play well for you or not. I knock all my bats and oil them, I spend hours doing this to every bat, some don't even get used for the season as I am not satisfied with the knocking so will work on them the entire off season.
Right now I have 3 bats that I know are absolutely guns, or going to be. My Blueroom LE (Has been used in almost every game for last 2 seasons), BB Butterfly (Used in 2 matches, knocked in recently) & my RPC puchased shortly before the BBB but has not been used. Compared to my Salix, which is a phenomenal bat but just does not have that same feel, friend used it and loved it, for me though not quiet the right bat.
So i think it is possible to guess on performance at the start of life of a bat, obviously some bats will be the exceptions and that's Okay.