These works, which can be found via a search of original_medley_collab songtags:>1, should be tagged with their original medley, rather than all song tags individually. On the tag page for the medley, the respective relations can then be added for it. The rationale for this is two-part: 1) collabs may re-use the medley, which then makes finding works that use that medley discoverable, and 2) it reduces the amount of tagging on future works.

You can see an example of how this should be done here for reference (or simply search original_medley_collab songtags:1): ひとりぼっちの組曲

@__tacoguy @Moltern I believe these works linked here were added by you, so just bringing this to your attention.

Note that currently there isn't a simple way to, say, search for works that use a specific song, but that song is contained within a medley, and thus not tagged directly on the work, but this is a feature that is intended to be added in the near future.