In case I croak!
I don't plan on 'pushing up daisies' in the near future but, to help my daughter, executor:
Even railroaders aren't going to know which engine goes in which box.
Beside the inventory of engines, I just spent all morning labeling the outside of the boxes with the cab engine number so one knows what engine goes in which box.
I put 'not painted' on those, well... not painted!
Those with DCC have also been marked and manufacturer's instructions included in the box.
I used 'wall safe' tape so easily removable without damage to the box.