Most of Birth by Sleep seems to have been forgotten, so I wouldn't be surprised if that was one of the things forgotten.
But if all of this was forgotten, this furthers the belief that Goofy was not capable of making a fair comparsion. If he forgot about the keyblade, then he still shouldn't be able to call a kid a Keyblade master (In skill) after he just picked it up.
Kingdom Hearts 2 may be more recent in the Kingdom Hearts timeling but, Birth by Sleep is more recent in designs and story develpoement so, if the recent scans show images of they're keyblades with keychains then I assume that they have now designed keychains for they're keyblades.
Unless those keychains are different from the ones Sora gets. It could be they have been getting them from their master. They might have not been able to create themselves, since the keychains look exactly like the one their master has. The ones they have may have been crafted by their master in order to allow his students access to different keyblades and become more powerful. The fact the keychain has yet to change even though the keyblade it's self does is the only thing that makes me think they don't have keyblades and are not full masters yet.