Coro Duette trademark first used 1929

Was digging through trademark records today, and found the record showing that Cohn & Rosenberger (Coro) trademarked the name "Duette" in 1929, stating that the Duette mark was first used Oct 10, 1929

Seen in a 1935 ad - Duoettes v Duettes

In a 1935 ad for Coulter Dry Goods Company in Los Angeles. A drawing of a generic "Duette" type pin, described as "two clips that may be instantly transformed into a brooch...available in many striking styles". It is called a "Duoette Clip". No manufacturer or brand is mentioned, so perhaps a play on the Coro Duettes available at the time - or perhaps a misprint, since this was during the time that the Coro Duettes were being introduced.

Duettes that aren't Coro?

In browsing the book American Jewelry Manufacturers by Dorothy Rainwater, I found reference to a company called "Certified Metals Company". In the description it shows a logo that says "Loves Duette" for wedding rings and engagement rings, and mentions an ad from 1978

Given that this brand was used for fine jewelry, and apparently generally for rings, it will probably not cause any confusion in identifying pieces that we may find, but just in case, I thought it might be good to know that the name was actually used for items other than Coro.