I stumbled across this image here and ignoring the weird assertion that this is responding to (Of course women grew up on Star Wars), I was curious: would this costume have required a viewer with non-insider knowledge to fabricate it out of memory? It would certainly be possible to sit in the theater (perhaps a drive-in) with a sketchbook and take notes, but I imagine that there would have been promotional materials of the pilots such as lobby cards, magazine photos, and newspaper articles.
This is the only poster I could find of the pilot costume, and even then I’m not sure if it was from '77.
So purely academically, is there evidence of Rebel pilot images appearing in print in 1977?
JEDIT: I found a set of oversize character portraits that were available at the time from here, one of which is of Luke in uniform, and another which contains the full uniform from the side.
Notably, however, the high-quality image of Luke is reversed so anyone working directly from that image would have to have other reference for that and the helmet.
Finally, Marvel Star Wars comic #5 has many views of the Rebel pilots, and the comic released on August 10, 1977. Obviously they are not detailed enough to work as reference for the costume in the original photo.
So my question remains: Would there have been a high-quality reference of Luke in uniform to base a costume off of, or is it more likely that she did drawings (or snapped a polaroid of the screen?)