Yeah, unless one worked for Electrolux—especially in R & D—we can only hypothesize the reason for changes and upgrades.
The upgrades of which I am aware from the 1401 to the 1401B Olympia Ones are:
1) Bumper fins to aid movement on other surfaces
2) Wider wheels for easier movement on thicker carpets
3) The short front handle for easier vertical carrying
The 1401 was a repainted Super J introduced in the spring of 1979 which transitioned to the 1401B in the fall. A year or so later, the hose was improved with a vinyl cuff at the hand grip like the commercial hose for the Model CB.
_____
The 1984 (anniversary year) DJs had a couple differences from the '85s, '86s, & '87s: they came with the model name decal (along with the Floor Beautifier 1522) and pin-striped bumpers & wheels; although there were likely some transition cleaners with the pin-striping. Later shampooer-polishers of the period bore a 'Floor Beautifier' decal.
_____
The black-covered PN5, 1983-85, was made to complement the Silverado Deluxe and the contemporaneous Deluxe Special 1453. The cover was changed to 'light sand gray' to match the Diamond Jubilee 1521 and contemporaneous Deluxe Special 1453. The PN5C, with a 3-wire cord for the CB2000, also had the two colors of covers.
The PN6, 1986-87, bears a jade-colored cover, matching the secondary color of the Diamond Jubilee & Deluxe Special. The PN6A, 1987-89, which came with smaller rear wheels and modified air channels, came with the light sand gray covers for the Marquise/taupe 2100/taupe L-E & Grand Marquise/Model 90 and the jade-colored cover for the central vac. The 6B, 1987-89, for automatic tanks, & 7B, 1987-89, for non-automatic tanks, were equipped with the light sand gray covers for the plastic tanks (except the taupe line). The commercial versions were 6BC & 7BC. The labels were different for most model names.
