It seems to me that Vader in Ep3 shouldn't have looked exactly like Vader in Ep5. Shouldn't Vader have had something akin to a crude Mark I outfit, then by the time he appears in Ep4 20 years later, there would be some advances in the suit to improve quality of life. He would then be wearing a Mark III type of suit.
It seemed more like they did this for the 'Look, it's Vader!' effect.
In fact, Ep3 felt a bit like 'The gang's back together' with the marketing, but I digress....