Star Trek Cover Illustration

It's a mystery whether these pictures have ever been published. I got them from someone who bought them directly from Gimenez's wife at the Comicsalon in Erlangen. According to her, they are covers for one of the myriad Star Trek paperbacks that existed in the 80s. I could never find the book in question, and I've been looking for it for a while. I think it's probably unused designs, or illustrations for anthology editions. It will probably never see the light of day.

Signed by Juan Gimenez and a lot of informations for the print