That is very true. I printed a double portrait a while ago, and I was sure I had the negative upside down in the contact frame, because I distinctly remembered the man being on the right and the woman being on the left, though they would be reversed in the print. I had the notches in the right place, though, and the emulsion was toward the paper as it should have been. I was clearly remembering the groundglass image, and not the real orientation of the scene.