IM not so sure about "limited production" in so far as being a leading sales tactic, but they were limited production quite literally because of their time line history and appearance in the Numatic family.
When I was a student and did a short stint of commercial cleaning for companies, NUVACs were basically Numatic's commercial name. I have used a few NUVACs in terms of the bowler hat style offered on Henry for example; the NUVAC name is just an early name applied to early machines for the commercial market.
Almost all NUVACS I have seen feature the more open top arrangement like yours although the bowler hat ones I used years ago were also actual NUVAC branded models. The Numatic James is the "domestic" version of the NUVAC you have and has a fixed unremovable cord and originally wasn't as long as the one fitted to Henry. The James also had a fairly shorter hose originally (compared to 2.5 metres on Henry) and came with aluminium tubes as standard.
Regardless of the actual name, end of the day they're all Numatic - and they do last for years on end.
