I located Penncrest vacuum cleaner newspaper advertisements that indicate the sales span from 1964 to 1971. The only one that had a special model name was the Air-Jet (aka Hoover Constellation); Eureka's Lightweight stick vac used the same model name; but the others just went by the type of cleaner.
Here's a representation (there were others that contained the same models):
1. 1964 May 25 TOLEDO BLADE—Hoover Convertible-style, Constellation-style, Lightweight, shampoo-polisher, tank, Pixie-style
2. 1964 Jun 24 SPOKANE DAILY CHRONICLE—Hoover Constellation-style
3. 1965 Sep 19 - HERALD-JOURNAL—Hoover Convertible-style & Constellation-style
4. 1966 Sep 20 SARASOTA HERALD-TRIBUNE—Air-Jet text ad
5. 1967 Sep 28 HERALD-JOURNAL—Hoover Convertible-style & shampoo-polisher
6. 1968 Jun 12 SPOKANE DAILY CHRONICLE—Hoover Convertible-style, shampoo-polisher, canister
7. 1969 May 7 OBSERVER-REPORTER—Hoover Convertible-style w-round cord reel, shampoo-polisher, Eureka Cordaway-style canister
8. 1969 Oct 17 ST. PETERSBURG TIMES—Hoover upright & Eureka Cordaway-style canister
9. 1969 Dec 3 PRESS-COURIER—Hoover Floor-A-Matic- & Dial-A-Matic-styles, Eureka Mobile-Aire-style
10. 1970 May 6 PITTSBURGH PRESS—Eureka Lightweight & Princess-style canister
11. 1970 Oct 11 VICTORIA ADVOCATE—Eureka Princess-style & Hoover Convertible-style (squared hood)
12. 1970 Oct 15—Eureka Princess-style canister & Hoover Convertible-style
13. 1970 Oct 27 BEAVER COUNTY TIMES—Imperial washer & dryer; Eureka Crown Princess-style & Hoover Convertible-style
14. 1970 Nov 11 VICTORIA ADVOCATE—Hoover Convertible-style w-square cord reel & Eureka Princess-style
15. 1971 Jul 6 WAYCROSS JOURNAL-HERALD—Eureka 500 Series-style canister















Here's a representation (there were others that contained the same models):
1. 1964 May 25 TOLEDO BLADE—Hoover Convertible-style, Constellation-style, Lightweight, shampoo-polisher, tank, Pixie-style
2. 1964 Jun 24 SPOKANE DAILY CHRONICLE—Hoover Constellation-style
3. 1965 Sep 19 - HERALD-JOURNAL—Hoover Convertible-style & Constellation-style
4. 1966 Sep 20 SARASOTA HERALD-TRIBUNE—Air-Jet text ad
5. 1967 Sep 28 HERALD-JOURNAL—Hoover Convertible-style & shampoo-polisher
6. 1968 Jun 12 SPOKANE DAILY CHRONICLE—Hoover Convertible-style, shampoo-polisher, canister
7. 1969 May 7 OBSERVER-REPORTER—Hoover Convertible-style w-round cord reel, shampoo-polisher, Eureka Cordaway-style canister
8. 1969 Oct 17 ST. PETERSBURG TIMES—Hoover upright & Eureka Cordaway-style canister
9. 1969 Dec 3 PRESS-COURIER—Hoover Floor-A-Matic- & Dial-A-Matic-styles, Eureka Mobile-Aire-style
10. 1970 May 6 PITTSBURGH PRESS—Eureka Lightweight & Princess-style canister
11. 1970 Oct 11 VICTORIA ADVOCATE—Eureka Princess-style & Hoover Convertible-style (squared hood)
12. 1970 Oct 15—Eureka Princess-style canister & Hoover Convertible-style
13. 1970 Oct 27 BEAVER COUNTY TIMES—Imperial washer & dryer; Eureka Crown Princess-style & Hoover Convertible-style
14. 1970 Nov 11 VICTORIA ADVOCATE—Hoover Convertible-style w-square cord reel & Eureka Princess-style
15. 1971 Jul 6 WAYCROSS JOURNAL-HERALD—Eureka 500 Series-style canister














