Hi Broomvac!
Interesting question. We can’t really date this kind of Eureka upright based on the shape of the motor hood - that profile was introduced way back in 1973 and continues to be used by Sanitaire to this day.
The key indicator of the age of your Sanitaire is the logo and graphics. I’ll do a bit of research, but I would guess that I began seeing the Sanitaire blue line in vacuum dealers in the late 1990’s. And that swirly Sanitaire logo is relatively new as well.
One other indicator is where it was manufactured. At some point Eureka’s parent company Electrolux moved assembly of all uprights from Bloomington, Illinois to Juarez, Mexico. I think that happened around 2000-2005. If your Sanitaire says “Assembled in Mexico”, than it is from the last two decades. If it says Made in USA, it’s probably from the 1990’s.