There have been reports by some collectors that some of the earliest self-adhesive issues from the 1990s have lost their adhesive power and they are coming off of the covers they were applied to.
To be honest, I donít think anyone knows for sure how long the modern self-adhesive stamps will last before losing their adhesive power. Will they loosen in the next 20 years? The next 50 years? Who knows? It seems logical though that at some point in time, the adhesive power will lessen over time to the point where they may fall off of covers.
This will create an interesting dilemma for postal history collectors. They may have to, say, hinge the stamps back in place on the cover. Lining up the cancel lines will be a little tricky.
What about collectors of mint stamps? Will the stamps still be considered MNH if they lose their adhesive power and separate from their backing paper?