Well I just did a search on PVA gum here and found the following from a post in 2009. Looks like a bunch of my Swedish stamps are in fact mint. "In the last 30 years, Swedish stamps
have a gum that is nearly impossible to see.
Most other countries are either using self
adhesives or old fashion water activated clear
gum which you can see and feel.
That is the first I've known about PVA.
Thanks all for the feedback.