https://janetdocs.org/joy%2fdb%2fgroup-by and https://janetdocs.org/joy%2fgroup-by both exist. Upon importing joy, both variants are available but only joy/group-by has documentation (because the extended versions aren't :export true internally).
The core issue's that an example only refers to one version.
As they're undocumented, removing or perhaps symlinking the extended forms might makes sense - but both work in code so I don't know how to avoid this situation.
Widening examples to optionally refer to multiple functions could work - indeed, it would allow interesting examples relying on multiple to "tag" them all. Of course, we don't want anything using common things like string to pollute string's page.