I think flipping and editing a shot from a different movie is fair game because Lucas did it for the SEs. Spot the differences!
These are both from the 2011 Blurays by the way, highlighting the oversaturated grade that ROTJ release had, and also the DNR present on that TPM release (which unfortunately persisted to the latest releases).
Yeah, it is super common to Blockbuster movies reuse shots from other previous movies, but we have to use this notion wisely because it could look lot fan-editty if not well done.