Oh, now I get the convertible thing. A little slow here. Completely different concept (pardon the pun) than the orig. Convertible. The Hoover Dual V, which was the second name used on the V2 model, had versions with both types of dirt cassettes. At that time, they didn't capitalize on it from a marketing angle. The bag cassette that took the (expensive) polyfiber Hoover Y series bag was the bonus. The regular models that came only with the bagless dirt cassette had one model number, and the same exact machine that had the bonus bagged cassette had a different model number.
Over the years, I've found several of the bonus bagged containers in the junk bins at thrift stores, complete with a new, unused bag inside. When I sell a refurbed Dual V occasionally, buyers decline the bagged cassette.
The V2 and the Dual V (the models with the four, diagonally opposed mini agitators, have better electricals than the later Savvy. My understanding is that the Savvy with a single agitator was a rework of the Dual V because they'd had so much trouble with the latter. Actually, the early Savvys were still equipped with four agitators. Unfortunately, some of the changes that they made on the single roll version were not for the better. Incorporating the control for agitator on/off function with the basic power switch on the handle was more convenient, but the switch on the Savvy is a weak link and a replacement costs $20-something. The contact points inside the switch burn out (in my opinion) prematurely. The earlier Dual V with the agitator selector switch on the floor nozzle is less convenient but more reliable.
The "dual vee" concept has to do with the suction at the nozzle being from two passages in the nozzle rather than the conventional single one. As built, the two passages are both more narrow than typical single designs. The plenum where the two meet is articulated which complicates the design a bit, and the plenum outlet is a right angle, not the best design.