The 1967 brass halves were in both the proof-like and proof sets, Roy. Prooflike were shrink wrapped in plastic cards and inserted 3 cards to a page in blue 3-ring binders. Proof tokens were in red Dansco binders with sliding covers over the tokens.

If you have any of the FM sets, it's probably time to remove the tokens and re-house them in a more stable binder. The cardboard does tone the edges of the tokens, and I've seen some tokens that actually had the edges corroded by chemicals in the paper. These probably had some moisture involved, as many of the sets are still OK.