I will add a little to this, the staining to the stamps is not as dramatic as the album pages, the stain is very pronounced though. As I stated not all of the blocks are tainted, some more than others. My best guess is that these were mounted some time in the mid 60's to 70's.Just a guess though, the photos of the remaining mounts
show the different phases of deterioration. The upper "self stik" mounts
show heavy browning, the crystal mounts
are all showing different shades of yellowing and browning.I do not know how these were stored over the last 25 years or so. So here are examples of used on pages with stamps and unused and still in the original packages.