I know what your are pointing out, but you have to understand... MANY bands tour in front of records to be released, so my poster does work. Floyd touring the Wall in 79 is 100% fine. Wall themed art is also fine. I found out that The Wall's promotional materials started to hit record stores in September of 79.
They toured the Wall in Feb of 80, so a couple months difference in a fantasy line up seems to be ok to me. Point is, they were huge enough to headline, with or without The Wall in the can. In October of 79, we can safely assume that record was finished... so they are on my poster, and The Wall art makes sense.
The research I'm talking about is more along the lines of having bands that don't exist yet, or dead people, or good ole headliner worth.