That's a bit of screwy logic, or careful word-smithing on their part, that completely screws the principle of the NFA trust in the first place.
Only those that are ON the trust at the time of NFA-Item Transfer (i.e., stamp-approval time) are allowed to single-possess that item.
So, if I have a grand-kid, and 21 years down the road, I want to add him to my trust - he can't touch shiit by himself, even though he'd be one of the Trustees...
Fucked up...