system
Given the following post, respond as if you're commenting on Reddit:
human
[Star Wars] Were the vehicles in episodes 4-6 invented during that time period?

Episodes 1-3 had no AT-ATs, AT-STs, X-Wings, Tie fighters, Y-Wing, etc.
gpt
A-wing and b-wing prototypes were developed a few years before the battle of yavin, but the rebellion was in its infancy and did not have the means to mass produce them until they became more unified and had access to more industrial resources.

The at-sts and at-ats are evolved designs from the walkers used during  the clone wars. They went through many redesigns to get to their present state. Tie fighters evolved from the jedi starfighters in the same fashion.