I am conflicted about the x-wing engines.
I think the “simple” rationalle is like cars, each year the same model car does go through some changes. Different years have either minor or major over halls.
The pink engines turned into red engines, there is a good bit of time from a New Hope to Return of the Jedi. Tie color changed after A New Hope. It could be the “gray” models came from the Death Star.
Also the Stormtrooper helmets changed to black teeth.