First of all, how do you pronounce that?
Mainly, though, I want to thank you for sharing your background information. I appreciate that your knowledge of wine industry terminology is superior to mine, and hope I haven't made too big a fool of myself.
As you said, "[m]ost sparkling wine producers (in the US) have moved away from using the word 'Champagne' in their nomenclature". As I indicated, this trend has been supported, in fact goaded, by legislation. And, of course, US winemakers are further motivated to conform to international protocol by self-interest, namely, their desire to have the AVAs recognized and respected by the worldwide community.
Nevertheless, the broader definition of "Champagne" has been embraced by the public at large, and this is reflected in our dictionaries. Similarly, the medical community has a strict definition of "paranoid", and the general public has another. Most of us will use "paranoid" to mean "having excessive distrust or suspicion toward others", and our dictionaries support this usage. But mental health professionals tend to bristle at the use of the word to refer to anyone but a person who is afflicted by a specific type of psychosis. They can become positively irate when a layman calls someone "paranoid" who has not been so diagnosed by a medical doctor. It's like they think we're out to get them. Frankly, these people need help.
But I digress. My point is that it is natural for a wine industry professional like yourself to advocate the more narrow usage of terms like "Champagne". But to call the broader definition incorrect is to deny the evolution of the language.
Similar things happen with brand names. "Aspirin" and "Heroin" used to be trademarks of the Bayer Corporation, but have long since fallen into generic use.
I believe it was less than a year ago that I found out that "Realtor" is a registered trademark and, as such, must always be capitalized and can only legally be used to refer to someone who is a member of the National Association of Real Estate Boards.
Perhaps it should be a requirement that Champagnes that are not from Champagne be spelled with a lower-case "c".