In practice, the difference between base used and traced (On our site both are treated the same, although they are tagged differently) is entangled in all of this, too.
Edits are derivative copyrights. Bases made from someone else’s art is treated as a trace - it is an edit. The original artist retains their rights to the base/trace/edit.
Images that are then made from a base are another step of derivation - they are also edits, and the original artist retains their right to the image made from the base.
The person who made the base has no rights to the base, except that they may ask to have their base deleted. The original artist whose art was used to make the base may delete the base if they choose for being an edit, and sometimes they ask to have things made from the base deleted, too.
So, whomever makes the base isn’t so much an artist on this site as an editor, and they do not have a unique copyright to their base, unless the base is a unique work of art, in which case we tag them as an artist, because they have a uniquely copyrightable work of art - just one that is a base.
So, I don’t know that tagging the maker of the base is useful. The people who must be tagged I think are the original artist whose work was used to make the base (or the base maker of the base was an original work of art) and the person who made something with the base. Both of those people on this site are tagged as artists, and the “base used” is treated as a derivative work so it should be tagged as an edit (although this doesn’t always happen - it depends on how the original artist feels about it most of the time).
Does that help? This is just how it’s handled from the standpoint of takedowns and DNPs, so I don’t know if it helps.
For what it’s worth, “Based Used” is a bad fit for this site in many ways, because of how we handle copyright, DNPs, and takedowns.