I just bought a handful of Buick posters from a guy and it included this GNX poster. I've seen this poster many times but never seen this variant of it (no GNX grill emblem and big GNX logo on poster).
I've never seen that one either. It wasn't issued by Buick. They only printed the one that I ever known of. Here is an interesting piece of info for those who like odd information. The picture used for that poster was taken at this location 42.925383,-83.617222 - Google Maps (dead end street off of Perry Rd) The GN used was driven by Chuck Jensen. Photo taken by Gary Smith (Buick Photographer). I have the picture that was taken just after the one used (little to much SMOKE).