Actually, when they dip riflescopes or any other optics, they fully strip them down to a bare tube so that there are still no exposed edges to the film.
I think tat if you have an exposed edge, moisture 'can' get under the film & lift it off. I once had a dipped rifle (many years ago) air that I scratched up pretty badly. As soon as it got wet I noticed the film started to bubble. Now, whether that was down to the film, the process, or the surface preparation, I couldn't say.
Give them a call & get it straight from the horses mouth.