Well I'm no expert, but in my opinion as an ex-Kirby dea
all I can say is I would consider any Kirby up through the Sanitronic VII to be a 500 series Kirby. The DS50 was the first Kirby to have a two speed motor, as well as introduce the Rug Renovator. The only difference between the DS50 and the DS80, besides color, was the handle fork. This handle fork was the first to become a standard through the Legend II. Of course the DS50 through the DS80 had the exact same motor. The Classic was the first redesigned machine and had the first 6 amp two speed motor, and introduced the 16 inch wide rug nozzle. The Classic Omega through the the Tradition had improvements to the motor, and the Tradition was the first to have a disposable bag. The Heritage through the Legend II had motor improvements as well as slight differences in the handle grip, and improvements on the disposable bag system. The Generation 3 was the first model to introduce the Tech Drive, and all models after that are refinements. I bought an Ultimate G Diamond Edition, and love it. I thought about trading it in on a Sentria, but felt the UG DE is a better model, and in a way, the Sentria was a step backwards. I don't know if this helps, but that's what I think.
Joe.
