The inclusion of a pn was probably the acknowledgement that anyone spending money on an Electrolux in 1982, was expecting it to have a pn. By 1982, wall to wall carpet was EVERYWHERE. It was no longer the hardwood floors and short pile carpets of the 50s and 60s. Even other vac manufacturers were going to extreme measures to pair a pn with their cheapest canister.
It's interesting to see the evolution.