There’s nuance to be honest, or there should be. A lot of obscure snails in the southwest have common names that make a lot of sense eg “Cuyamaca shoulderband” which only lives in the Cuyamaca mountains, and most of these names were essentially made up by one author (or set of authors) when they were described. I think these species greatly benefit from having intuitive english names like that. And while it’s against inat guidelines to do this, would I have a problem (if the guidelines didn’t exist) with someone adding an intuitive name like that to some random nameless invert? Not really.
A much bigger pet peeve of mine for iNat names than inventing them is when multiple things have the same generic name because it causes massive amounts of misIDs. I constantly run into this with agaves/yuccas, right now there are two different species with the common name “Pulque agave” and I’m probably going to remove one of them for causing mass confusion
But common names are names people actually use. In scenario 1, if the name is actually in use right now, I’d say it’s valid even by guidelines even if the original invention of it years ago was on iNat - at the end of the day every single common name was made up by someone out of thin air