They're clearly stated as being RZ-1s
This just seems to be an earlier version
At the moment, the Databank does say that the OT-era A-wing are faster and more "stripped down" (shields, armor, etc) than the Rebels-era models - though that's more "refit" than "new design":
http://www.starwars.com/databank/a-wing-fighter
As the Empire ramped up production of both standard TIE fighters and experimental models, the Alliance responded by seeking a starfighter that could outfly them all. Alliance techs turned to the A-wing, which had proved capable in early battles against Imperial forces. Refinements made by rebel techs stripped away the A-wing's shields, armor and heavy weapons in favor of raw speed, resulting in a fighter that was tough to maintain and fly, but could outrun even a TIE interceptor. These reworked A-wings played a large role in the Battle of Endor, the rebels' greatest victory over the Empire.

