Just curious because I don’t know the answer: can others ever be in possession of your non-trust owned items without doing a transfer / stamp process?
No. This was one of the benefits of a trust. You cannot loan your suppressor/SBR to someone else.
<edit> Someone else can USE it in your PRESENCE... but the owner of the stamp has to be physically present. Thus, the idea that multiple people in control of a trust could use an item covered under a stamp issued to a trust SHOULD be ok.
Again... not a lawyer - but this is how it was explained to me BY the lawyer who wrote my trust.