Here's a question.
Re 70s issues that are 'scarce' one thing that I've noticed and it doesn't matter whether it's Atco, Epic, Columbia, Mercury, RCA, 20th Century, Polydor etc. The rarer issues are normally on styrene whereas the demos are on vinyl. Originally I thought this was because they were using the Columbia pressing plant or released only on the west coast, but as I've got more and more of them I wonder whether it was a deliberate policy to make the demo's more longer lasting / robust?