I dont believe its outdated its just states you have to own the costume specific to the detachment. I do have (own) and troop with both TK and TD costume (depending on my mood, if I feel like humping that heavy backpack or not) so thats not a problem. I don't believe it matters what your Legion designation begins with as long as it can be verified that you do own the costume in question and mine can be verified easily (just by looking at my signature there are 2 examples of my TK).
I believe the more names you can get the better though. It shows there is a serious interest in this detachment and shuts up those that says there shouldn't be a TK detachment as there is no need for one. Just this last weekend we were doing an event with a trooper that was doing his first event and he was litteraly falling apart all day long. He definatly could use a detachment like this to get it together and improve his costume.
One other thing, I can not get into the 501st only section still. Is it possible to look into this? Thanks.