I was informed to make a copy of my original Form 4 and carry it with me whenever I was in possession of my NFA item. The copy is in a ziplock bag and stays in my range bag so it's always there if by chance I get asked about it at any of the ranges I go to.
You may know that the SBR, Full Auto, or Suppressed weapon is totally legal. Your shooting buddy may know the same thing. But the range officer or local Policeman may not, or may think your supposed to have the Form 4 with you at all times.
I'm not sure what the actual "law" is regarding having the From 4 with you is, but to be honest, it's way too easy to make a copy and carry it with me than to cite legal statues to some concerned officer.
I reject your reality and substitute my own.