I still think the current wording is clear enough, personally. We don't want to restrict uploads to only "official channels" with a symbol because I've seen plenty of official artist channels which are not "YouTube Official Artist Channels", plus plenty of officially uploaded videos which are not on an artist or label channel. For things like dodgy Spotify releases, I think it's already ok to remove those if we find them, but changing the wording won't help here because most people will have no idea how to tell if an upload is legit - it seems better to just assume it is since that's true in almost all cases, and act when they're found not to be.

We could add one sentence to the guidelines section if someone can offer something that would seem useful and clear, let me know.

Not necessarily. Unauthorized content sometimes slips through the cracks, even on otherwise legitimate platforms.
The obvious example is unofficial YouTube uploads, but occasionally unauthorized music finds its way onto more dedicated streaming platforms as well. These instances are often difficult to sniff out; we the listeners often don't find out unless an artist or label speaks up.
For example, I know this is unauthorized thanks to some research into the label who released it.

The description does already say "can be legally streamed for free" - if a site or an upload is illegal doesn't that already block adding it?