I’ve noticed that when uploading cover art, one of the possible types is track art, for situations when individual tracks have unique artwork embedded in each mp3. But this doesn’t seem to be an option for standalone recordings not associated with any release. Most of the time when a standalone track is uploaded somewhere like bandcamp, soundcloud or youtube, it’ll have artwork associated with it on the bandcamp/soundcloud page or in the youtube video - is there anywhere for artwork associated with standalone tracks like this to be uploaded so it can be used for tagging?
In the case of Soundcloud tracks with distinctive artwork or especially Bandcamp single-track releases I don’t see good reasons to not add it as a Single release. This also gets you all the other benefits standalone recordings don’t have (e.g. release dates).
I remember reading something in a style guide about this, but I can’t find it
I agree. For soundcloud and bandcamp: if it has artwork it’s probably a single.
For youtube: if it’s an official video and it has artwork then there is probably a single of the song to be found somewhere else.