I got the star wars soundtrack proof poster at today's propstore auction. And this appears to actually be a signed off one so the people who don't like to call untrimmed posters with color bars proofs can still call this one a proof because it actually is one. Interestingly the date is late June 1977.
Cool pick up, I had never heard of this soundtrack poster before. I didn't realize it was so rare until I read your post since it looks just like the OS style A. Congrats.
I agree with Thierry that there were too many things on linen for my taste at Propstore today (as usual), but I did win a folded copy of The Black Cat (1941), a minor Universal horror title that is very scarce (especially in unbacked state).