Quite a bit of Scepter was on vinyl, it depended on which pressing plant they used. Also have a few Wands on vinyl. The NY stuff (including Garrison presses) was mostly styrene. I think when they got stuff pressed elsewhere - like down south - is when you tended to see the vinyl.
The Humphrey Stomp above is an issue, the stars just there too highlight the A side, not indicative of a demo.