As of July 2016, Rule 41F was introduded which required tha:
So, as I undertstand it, that was the point where trusts became more onerous:
Background Checks for Responsible Persons (Final Rule 41F)
Note that this applies specifically but not solely to the event where "receiving (sic) an NFA firearm in the name of a trust or other legal entity as the transferee on a Form 4, or Form 5".
... all “responsible persons” associated with a gun trust are required to submit FBI fingerprint cards and passport-type photos, as well as notify the chief law enforcement officer in their jurisdiction that the gun trust is purchasing or manufacturing an NFA firearm.
So, as I undertstand it, that was the point where trusts became more onerous:
Background Checks for Responsible Persons (Final Rule 41F)
Note that this applies specifically but not solely to the event where "receiving (sic) an NFA firearm in the name of a trust or other legal entity as the transferee on a Form 4, or Form 5".