Good call. As far as I know, from its early days Hoover US stamped its serial numbers in the casings until switching to adhesive ratings tags in 1978 when the plastic-based Convertibles & Concept Ones were introduced.
It would've been nice if Hoover US had begun embedding the times of production into its serial numbers back in the '60s like Hoover UK, but that began circa 1987 (I'm unsure about Canada's).
Btw, Hoover US & Canada earth-tone colors (in Deep, Medium &/or Light) were Seal Greige from the mid-'60s to early '70s and Taupe from the early- to mid-'70s. Yours appears to be the former, because the darker color looks more like cocoa powder than brown sugar. If you're going for a matching Hoover color set let me know if you want to see a list I comprised of the models I found in those color combos.