Currently I am researching my next costume (Armored Jedi from SWTOR). I have noticed that a lot of people advertise "501st Approved" or "Rebel Legion Approved". One thing that has been pointed out in a bunch of the forums I have read is they may have had their design or costume they are selling approved in early stages of acceptance. Standards for costumes can evolve as better reference photos, action figures, etc become available thus making the standards a bit more detailed oriented. So I would always be careful when it comes to purchasing something "501st Approved". Technically the person wouldn't be lying, however an honest seller will give you a heads up that it may not meet current standards set forth by the Legion and to check with the Legion to see what would need to be done to meet standards set forth.