OK, big sponges can be found in (probably all) VICL 40XXX double CD cases.
I also found one in N64 Smash Bros album.
Here are some pictures of those, from the oldest VICL 40XXX album (1991) to the newest one i got (1994), and then S.B.
So yes, the material is aging even inside the case.
(and the stack of those smells like, ooold
)
Those were clearly added to prevent the disc, in the section of the case without booklet, from jumping off its case mount.
Actually the VICL 60XXX album i got, acquired new, not coming with a sponge as Victor apparently stopped including those at that time, had one of the CD unattached and moving in the case as i checked it, eh.
Not
much of a problem actually, as the disc can then only move away and back the mount in the case, not sideways.
And, if you ship such used big double CD case albums, you should always put some plastic bubble sheet in this space.