Starting around 1981, the power nozzle changed design. Also in 1981, Hoover came out with the Spirit line of canisters to supplement and later replace the lower-tiered members in the Celebrity line.
In 1982, they brought over from France the Electronic 1000 canister, which in Europe was known as the Sensotronic 1000. The power nozzle is definitely USA-made because in Europe the Sensotronic PNs do not look the same. Around 1984-85 this was finally replaced by the USA-made Dimension 1000, which also had two or so less-expensive models (e.g. Dimension 900).
~Ben