Thanks a million, @Simon_Arnold3 - I’m really glad I asked the question 
Another option would be adding them all to your library, sorting on date added (to quickly locate everything), select the files and add a dj mixes tag. At that point you can click the tag button next to Focus, above your library to filter them out or filter out everything else. You can also create a bookmark with the tag filtered out.
Use a tag editor to tag them in a way that makes sense to you but doesn’t clutter your DB. Maybe all dj sets are album=dj sets or something similar.
I’ve had a wonderful time sorting through my old random stuff by choosing ‘hidden’ in the focus menu. My household are none the wiser that there’s a load of messy stuff in the library. Every now and then I hop over to the hidden area and have a listen. Sometimes I find stuff I like and I group it together as an album via Roon and manually set some cover art. Sometimes I find stuff that sucks and I am now very excited to have discovered that Roon lets me delete files off my server via the ipad app. So now I’m cleaning up the crud as I go too. Awesome outcome. Thanks everyone.