Erik Pancakes said:
To be pedantic, it wasn't A New Hope until April 1981. So no one would have known to refer to it as A New Hope in 1980. ;)
The new title actually appeared in the published version of the script included in the art of Star Wars in 1979.
Personally I have no problem with the re-releases being referred to as A New Hope because that's what those versions are known as. I actually thought it was more disturbing having a re-release version being officially labeled by Fox as the original '77 film up to '95 as if nothing never happened.