The only restriction is the exact combination of the player's name and number. Not that this needs an example, but say your fictional Smith retired wearing the number 1. You'd be able to customize a shirt with the name Smith and any one of the other hundred available numbers (0, 00 and 2-99), you simply wouldn't be able to customize a SMITH 1 shirt. Alternately, if you fudged the name a bit (say, R SMITH), you could then put that on a shirt with no. 1. I know it seems ridiculous, but my guess was always that they were just protecting their rear ends so that no retired player could have a case that they were profiting from his name via jersey image (the exact combination of his name and number). The MLBPA licensing thing is serious business. For the rare player who isn't a member of the player's association (Kevin Millar, for example), that player's name and/or likeness can't be used in any sort of licensed product for this very reason, because the MLBPA doesn't have the catch-all legal permission to use it/them.