Old Sanding belts?

I am rebuilding an old cabbing machine that has apparently not been used for several years but it all seems to be in original working condition with original parts. It has expanding drums.

A full set of sanding belts of various grits came with the machine. They all appear to be as old as the machine and are in original boxes. The problem occurs when I put one of the old, but unused sanding belts on, start the water, and begin sanding a rock (220 grit.) In about one minute the sanding belt came apart at the seam. I put a second belt on thinking it must have been a fluke, but in about another minute the same thing happened to the second belt. It came apart at the seam.

I am sure these are the correct size belts for this machine and they are turning in the correct direction based on the arrow marked on the belt, and at the correct speed.

So my question is, do belts go old over time and fail because of old age? Or, is there something else to try that might be causing the belts to fail?

Belts are expensive enough that I don't want to keep destroying belts trying to figure out the problem.

{Jokes about things failing because of old age can go here}