Rodgcam - I had something similar happen to me a few years ago. I bought a Yemen #2 with cert from a French dealer on
ebay, and I didn't see it for a couple months. I am usually patient with international orders, and the seller did mark it as "sent" so I just figured it was just caught in the international mails somewhere since the tracking dead-ended before it left France.
One day, it arrived in the mail - the envelope had been completely soaked, and was opening on its own. When I found the stamp, it had also been in one of those black cardboard approval cards and had come out, so part of the stamp was against the plastic and part of it was against the black cardboard. The stamp is completely stained black (thoroughly) where it was not next to the plastic. It no longer looks like the cert (which is unreadable anyway).
There was no moisture barrier, and it would have had to be packed in a ziploc bag for protection since it was completely soaked.
The water soaking was the fault of either the French La Poste or the USPS, and the seller never answered my messages. But, lesson learned - for myself, at least. I now always pack my stamps well enough to survive being dropped in water.
Sorry you had to go through that, I also collect Russia and I know how difficult it is to find sets from that era in such pristine condition.