As well as this 2 explicitely different collector & genre groups with the same name... (as the current system allows us to...
):
Electronic
Bass Music
Bass Music::Genre
That's identical to what I am doing with Jazz both being a category and a genre. (see my screenshots)
There is no issue there.
I'm not saying there is an issue. But, entering/using it this way, even though we stated explicitely (in this thread in the past that it probably would be needed, or be best practice, to have unique names for a single tag hierachy, this act was a 'oh, let's just move the goal post a little...' notion for me

But, it seems to work indeed/despite and is quite helpful, and a neat additional angle....
As for:
Jazz
Bebop · Cool · Hardbop
Bebop::genre
Bebop::subgenre
I do not have that use case...and I'm actually not sure what I would prefer or if this should even be allowed
It was already allowed and it can be very useful. I don't see what problems could arise from it.
And for users having subgenre tags it is essential.
(and that is the title and the reason this topic exists ;-)
I don't think so that this was explicitely allowed, but it accidentially/incidentially worked. But, this also is moving the goal post a bit further.
It's not the fact that it uses Bebop::subgenre, that was indeed the point of this thread - but the fact that your outline case is attempting to populate the same named thing (i.e. the Bebop tag Hierarchy Group - be it 1 or 2 groups... which, if we don't know, this already screems something is askew), from 2 different source fields (::genre as well as ::subgenre) within the same TagHierarchy definition.
And this feels... odd...messy... & skewed.
But, this is just a hunch/feeling, not an opinion or a fact.
And for:
Slightly off-topic but curious:
So you are not writing genres sourced from Discogs to the Genre tag?
Does the actual Genre tag also have a place in your workflow and hierarchy sheet?
For me official Genre field is populated by hand-picked Genre descriptors that are true for me.
DISCOGS_RELEASE_GENRES & DISCOGS_STYLES hold the discogs auto tagger values and represent the discogs definitions (which can be great, but also terribly hit & miss...).
This allows me to see my library contents within 2 (or more) Genre Taxonomies easily, side by side, and it's awesome; especially since it comes for free as the discogs data has been added to most of my library over the last years

The only thing missing is generating MusicBrainz IDs from discogs IDs, to auto retrieve the MusicBrainz data as well, and plonk it into custom fields as well...
c.