[BigJJ]

From the aforementioned, it appears the same procedure is used for evaluating 40k and 125 model bats. With regard to the additional posted questions regarding game used bat evaluation in general - whether 40k or 125 or other model - the following is my understanding and my modus operandi:

First you determine if a 40k or 125 or other model is a professional model bat - does it have signs of being a store model bat - ie. inch marks, other signs of being a store model bat, etc.? If the bat does not have inch marks, other signs of being a store model bat, etc., then it is a professional model bat, perhaps made for the person whose signature appears on the bat, perhaps made for another major or minor leaguer or general team use.

Second, if you determine that what you have is a professional model bat, you then need to determine if such bat was actually made for the player whose signature appears on the barrel (because professional model bats bearing the signatures of the great players of the day were made for other major and minor leaguers and for general team use). So you determine if the bat is made to the specifications of that particular player, in the year or era in which the bat was made. In other words, in a given year/era, what bat length, weight, - and if applicable finish, knob style, etc. was the player whose signature appears, ordering - based on Louisville or other factory records - or if few or no such records exist, based on photos or other evidence.

Third, if you determine, based on the specifications of the professional model bat in front of you, that the bat was likely made for the actual player whose signature appears on the barrel, you then look to see if the bat was likely game used in general - and you also check for specific game use indicative of the player in question. Some hitters often positioned the brandings on the bat a particular way when they got up to bat, so the ball would more often than not make contact with the bat in a particular area. Some hitters scratched the surface of their bats - some wrote on their bats. Some put tar or tape or other materials on their bats.

Fourth, you then examine provenance to 'sure-up' or add or detract to what is factually in front of you.

Determining whether a bat was made for the player whose signature appears on the bat, and then determining whether such player used such bat in a game is really a determination of a percentage chance - at least for what I like to think of as the glass-negative era bunch - can think of as pre WWII - as you really need a photo, video, or writing by the player himself on the bat itself detailing use, for 100% certainty of use in a game, in my opinion (and a player detailing use is often not even 100% - as another post pointed out so well a few weeks ago).

That being said, if you have a
(i) a professional model bat
(ii) made to the player's specifications whose signature appears on the barrel, in that year/era in which the bat was made, and
(iii) there is game use
in my opinion, that is likely a game used bat by that player, and in the opinion of a good number I believe. If you have specific game used traits on the bat relating to that player, the percentage assuredness (is this a word?) goes up from there. But in my opinion, if you have the aforementioned three, that is pretty substantial evidence, particularly for the pre WWII and even perhaps pre-1980 players.

The above is my understanding and mode of operation; others may have different or additional ways of looking/reviewing.