Brian—thanks for the photo link, I never knew about that!
Owen—that's correct. The 702-A was the original "turtle" shape Princess that was launched in August 1961 and was manufactured through May 1964.
For some reason, Eureka Williams decided to go with the "trapezoid" shape for another Princess canister, model-type 705-A, beginning in December 1963; so there was an overlap in production according to the *shipping inventory list (through 1964) posted by texbodemer. That may have been a regional difference between the eastern and western divisions. There was even a short-lived Princess II model-type 711-A from Jan-Dec 1963. Although there was a variety of features and lid and handle styles over the years, that trapezoid shape was used for the Princess and Cordaway canisters (and Roto-Matic Power Teams) through the 1980s; although the Princess moniker was dropped in the early 1980s.
*Note: The shipping inventory list typically excluded model names.
>>The Model-Type 500-A, the subject of this thread, debuted in April 1963 and was made through May 1964.
To Eureka, variety was the spice of vacuum cleaners!
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Here are the series lists of the turtle and trapezoid shaped canisters by Eureka Williams/Eureka that illustrates that last point—
~500 Series Canister Types (from online parts lists), which likely included lesser known colors along with the more popular ones:
(Continued as the 3200 Series—no types list located. The 1240 Series was the Roto-Matic Power Teams.)
500-A/B/BDV/BE/BK/BKD/BF/BF A/BF H/BF HM/BFT/BFZ/BS/BT/BTD/BTV/ BTX/DFG/R/RB/RBV/RV
502-A/B
508-A
513-A/B/D
~700 Series Canister Types (from online parts lists - may be incomplete; a 'T' alone or with another letter typically meant that tools were included; a 'V' usually stood for "Vibra-Beat" nozzle; some models were store exclusives for which I found no ads, so this list is incomplete that way, too.):
(The 3300-3400 Series continued the line, but I have found no type listings for it so far. The 1250 & 1500 Series were the Roto-Matic Power Teams.)
702-A/AK/AT/AZ "Princess"
703-A "Prince"
705-A/AG/B/BD/BDV;BG/BV/BW/DG "Princess"
711-A/AD/AT/AV (A- for sure "Princess II" with new cord caddy and Libra-Beat nozzle; not positive about the other types)
711-B/M/MV/DD/F/F DV/F G/FV/T/X/XD/XR/XRG/XKL/XRM/XRV (no model namer as far as I've researched)
713-A/B (no model name)
714-A/B/BG/BV/SG (at least type A was "Prince II"; later 714 ads included no model name or type)
730-A/AG/B/BG/BV/OR "Cordaway"
736-A/AD/B/BF/BF D/R/T "Princess"
737-A/AR/ARG/BR/BRG/T "Cordaway"
738-A/B/BDV/BF "Princess"
739-A/B
740-A/AV/FM/R/T "Cordaway"
741-AV/BV
743-A
745-A/AG/B "Cordaway"
755-A/AD/ADF/AV "Princess"
760-A "Princess"
761-AS
765-A/AF/ASG/AV/R "Cordaway"
770-A/AV "Cordaway"
773-A "Cordaway"
780-A
It may be, too, that relabeled cleaners such as the Singer that Brian posted had two model designations - one for Eureka's books and one for the other company's (shown on the data tags).
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I hope that dark green 500-A will be purchased by a collector, as they're as rare as hens' teeth!