The organizations that you think are credible, are credible. The term is not legally protected.
Personally, when Subway calls their sandwiches "good", I think they are actually making non-good sandwiches, and they're trying to redefine the term.
Both "good" and "open source" are descriptive terms that are subjective. The OSI recognizes this themselves:
> "Open Source" is not and cannot become a trademark.
> there is virtually no chance that the U.S. Patent and Trademark Office would register the mark "open source"; the mark is too descriptive
https://opensource.org/pressreleases/certified-open-source.p...