Not original art (1950s/60s). Proof?

I bought a whole bunch of these online - they were described as 'proofs'. As this word is often used loosely I was hoping that they might turn out to be original art but they appear to be printed. I have put one up here anyway, with some more in the 'additional images', so people can have a look at them.

They are tiny (3.5 x 2 inches), about the size of old cigarette cards and are ink on card. Possibly they could be production art for some more mainstream, less explicit version of 'Tijuana Bibles'? Or perhaps someone here knows better?