I don't know what you mean by a common design style - there IS a common design style, but not based in the posters you're thinking of, which are all alternates.
The red Vader cover is not my chosen cover for Empire. It's an interesting alternate, certainly, but it's not the basis of my design style. It's a great poster and I'm glad it got used on something. Go Coov!
I don't know what you mean by the first Star Wars Classic Edition cover "I" did either. I never did a cover for Star Wars Classic.
My official poster for SW is the "wood" style one by Coov.
http://orangecow.org/starwars/swcovers-nonocp/classicwood-coov.jpg
My official Empire poster is the Japanese/Australian inspired version, either on snow and metal or on black.

My work on Coov's template. Coov would pick his "style A" cover over this one I think - but I didn't want to use the Style A, as it's the "common" poster and I'd chosen style D for Star Wars, I wanted a more obscure yet good poster. This proved a huge headache, as I don't have a good scan of the Australian poster anywhere. Still don't! The Japanese poster was altered to get the current version, and it took foreverrrrrrrrr.