I was able to get the Houghton Mifflin promotional letter that accompanied that Silmarillion poster.

Interestingly, I wrote to HMCo back in 1977 requesting info on the release of the book and received a similar form letter from them (which I now cannot find…)

Khamûl wrote:

The "year of S" isn't really a poster, as such; it's more of an A4 flyer which came as part of a larger promotional portfolio. It contained, amongst other items, another flyer with the contact details of all of the UK (& Ireland) "home" sales reps. There's probably discussion of it (on TCG) buried away somewhere.

Those photos are sooooo 1970s.

They look like they come from mugshots on The Sweeney

Adding a few more bits of ephemera that I have to the conversation