And I would argue that the trust doesn't own the SBR until it's approved, and the parts used to make that SBR could be bought/owned by anybody. Especially with the EForms system, most parts are paid for by an individual. The tax stamp isn't even paid for by the trust in most cases. (Some people do get a bank account, which is a waste of time, but don't have a credit card to use).

If you put the lower on the trust before it's approved, you've simply added a non-NFA firearm to your trust. No different than adding your 10/22 plinker, your regular concealed carry pistol or your favorite shotgun.

The trust can hold these items, but there's no requirement for it to be there. Bottom line is it works either way. Most people I know add them after the approval.

You won't be wrong or doing anything illegal whichever order you choose.

This is for the Form 1 SBR/SBS/etc. It is different for a F4, because you don't possess the weapon/suppressor until after approval, so you don't need to add it to the Schedule until stamp received.