Acryloid or Paraloid B72 is a copolymer of ethyl methacrylate and methyl acrylate and is extremely stable. It is usually used for marking dissolved in acetone.
Acryloid or Paraloid B67 is isobutyl methacrylate and is not quite as stable as B72. When used for markign objects it is usually used dissolved in white spirit so that it can be applied as a coating without disturbing the underlying number on the B72 application.
It would be better (for the longevity of the number) to use B72 for the base and top coats if possible.
Hope this helps.