Glen,

You really don't have to be paranoid about the celluloid rot that Kees is having to deal with. It can happen to any celluloid scales, but is generally more of a problem in high heat and humidity situations. The older the scales, the more liable they are to develop rot, but once it's started, it can affect other celluloid scales in close proximity to them regardless of their age.

Under normal use (if you have a rotation) you'll handle the razors on a very regular basis, and you can simply look them over carefully for any rusting, and sniff the scales occasionally to make sure they don't smell vinegary. If you notice them changing color, then you can have them rescaled.

If you have a collection that you don't normally shave with, it would be a good idea to check them regularly for any signs of the rot. This is not something that starts and causes great damage overnight. It takes a little while for it to progress.