some additional random thoughts, after a few more days of further thinking:
Medley is a very specific idea, when you think about it. It has to be a new arrangement, based on old compositions, newly performed for this specific purpose. It specifically cannot be a digital (or otherwise) combination of existing audio recordings. Given that fact, it seems that medley is a supported relationship just because that’s what has only been possible for hundreds of years. Let’s keep up with the times and add this new type of relationship for works!
If work relationships are added for mash-ups, I think it might logically follow that work relationships for dj mixes be to added as well. While it may be niche, there are some complex cases where a dj has added their own spin on a recording enough for it to warrant new work (both in my personal opinion, and in the opinion of rights societies). For example, the dj could have their own rapping or spoken word in the track, or little vocal samples from other recordings interwoven in the track, but at the end of the day, it is still a dj mix (mixes into the next track smoothly, uses crossfading, beat matching, etc.) of an existing recording. Right now, I am using “other versions” or “based on” for this, but this doesn’t seem right for the same reasons as I laid out for mash-ups.
I’ve been going back and forth about whether I actually agree with my own points here, mostly hinging on the interpretation of the “based on” relationship. If you take a more broad view, you might be able to accept that ‘based on’ should be used for mash-ups (or complex dj-mixes). The new recording, after all, does use the two original recordings as its “base”. The guidelines section does also say “This is used when a new work is based on or includes (parts of) another work”. Considering “parts of” is parenthetical, this does seem to read as “use this relationship when one work includes another work” (which is exactly what a mash-up is). I still cannot square this with the fact that the guidelines specifically say not to “confuse this with medleys, mash-ups, remixes, etc.”, but this is probably an oversight that we are coming to the objective conclusion about right now! (hooray!)
P.S. while writing the end of this I realized that when I was talking about a dj mix, I was really just describing a remix that happened to be part of a dj-mixed release (although the two ideas are very heavily intertwined for some artists, so it’s hard to say). But probably a “remix” work-work relationship, not dj-mix. But maybe both?