Welcome to the forum ausjack

From my own personal experience I have found the following countries difficult to soak: U.S., N.Z., Australia (some issues), France (some issues)
The ones I didn't have any difficulty with are: Canada,Germany,and G.B (mostly ok with GB but some newer issues like the large Machin labels are said to deteriorate if soaked)
I guess each individual collector may experience varying degrees of success. Some issues I know do not soak well I just leave on the cover or piece.
Hope this helps
Chimo
Bujutsu