You can get a red celluloid tape that is era correct and tape it from the inside. Nice set.
Oh. I've got plans
First this...
Next I'll lay them out on gummed paper tape to join the pieces as one again. Then finally put the piece right back in the way it was with adhesive as original.
Depending on my level of OCD at that moment, I may do the same at each corner, converting the paper tape under the printed top layer.
Alternatively I can just lay the gummed tape in each corner to be seen. I like paper tape with cardboard as it's original material, and easily reversible... if for some reason you want to take it apart again.