Where to start, where to start? How about with the pack itself:
Art Spiegelman drew that kids. He won a Pulitzer Prize in 1992 for his graphic novel Maus and that is just mind-bending. The back has the usual instructions for an interactive Topps set and a contents description that clearly states "cards" in the plural, although I only pulled a single valentine. The flaps were actually unsealed but I don't think the contents were futzed with.
Compare this to 1967's Nasty Notes pack:
You can't really see it but the top line has a Brooklyn address and not Duryea, whcih matches the Brooklyn in the penultimate line and the illustration is identical on both versions, down to the "Nasty Notes" reference.
Here is an unfurled wrapper:
As for the Nasty Valentine Note proper, it appears to work two ways:
The "payoff" side is very colorful:
I am toying with the idea the set is so hard to find due to its being sold in head shops. I'm really not sure about that and the various Topps Valentine's and Hallowe'en themed sets are always tougher than most, as are the paper sets and the metamorphic sets, etc but these are really hard to find and not a lot of people know about them, not even some very advanced non-sports collectors. A full set would be very difficult to put together in my estimation and on the scarcity scale, it's almost test-issue like, although we know it wasn't.