Ben, I highly doubt that nozzle is a prototype. If it WAS, it probably would have never made it to any brochure for the lineup. I think the more likely answer for it's scarceity is most likely this nozzle belonged to a TOL model....and since Eureka wouldn't have sold as many of that model, hence the nozzle isn't as commonly seen as the MOL & BOL models nozzles. Another possibility is that Eureka could have discontinued the first nozzle design early in the production years of that canister, so again it's not as commonly seen as the second nozzle design.
Rob