Prolux Line
Good information from human.
Here are some additional details:
The Prolux series was introduced in 1987 with the 3rd model of the Discovery II. The Electrolux wordmark with the bold serif letters indicates that it was made at the Canadian factory; although it may have been assembled in the U.S.
The line included seven different models that had changes or upgrades including motors (you will find the model # in in small print with the specs on the brush roll hood when you release the handle). In addition, there were four different labels. I'm not sure if the Prolux and Prolux Plus cleaners were sold concurrently or not, but it would have been logical to give customers an option.
Here's a list of labels and models:
Prolux Commercial - model 1572E (8.1A); 40' 2-wire cord
Prolux - models 1572C (8.5A), U111A (10A); 40' 2-wire cord
Prolux Plus (w/onboard caddy) - models 1572G (9.5A), 1717C (10A), 1747 (10A); 40' 2-wire cord
Prolux 2000 - model U136B (8.5A); 35' 2-wire cord
Interestingly, the model 1572E also had these standard household labels: Discovery II (3rd of 3 models), Discovery Plus, Discovery III, Discovery Advantage, Regency Series, and Special Edition. I'm guessing that it was the first Prolux, and that Electrolux decided to take off the "Commercial" descriptor in succeeding models, because it really wasn't commercial grade (3-wire cord, reinforcements). The "heavy duty" descriptor that followed likely denoted the double-insulated 40' cord.
The Prolux cleaners were marked "For Household Use Only" on their name stamps, so they were likely marketed to home cleaning companies, individual home cleaners and home business owners.
In addition, there was a ProTeam label and models:
Prolux by Electrolux - models 1400, 1400X, 1400XP
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If you're interested in an onboard caddy, check some Aerus dealers for NOS or trade-ins. I've found some that are willing to network for customers (contacting and purchasing from other dealers). Fyi, be sure to specify that you want the caddy with two wand holders in gray or they may get you a light colored one or a gray one with one wand holder, which was made for the commercials, because of the placement of the power switch.
Aerus discontinued the onboard caddies at least 5 years ago when the current black line was launched.