General question of splitting a variant

I regularly see notes that either hasn't got any variants added, or have too few (perhaps) variants. (current note is an example - it has a SN black variant with a GrM reference in the comments) but there are multiple GrM references besides this which have a black SN. Now - because the comment contains a reference to a distinct version, people may not have added other SN black varieties to this entry - but they may have, given it is the only SN black variety added)

Let's say numista users have added their notes to the single variant listed (not knowing or caring) about sub-variants. How would one approach narrowing this main variant down when adding more variants? 

If you rename the existing, too broad, variant, then people will have an incorrect reference in their collections. 

How do Numista tackle this scenario? I have seen many notes with a ? first variant - is this a result of keeping existing notes “correct” while adding variants?

I have submitted a modification suggestion for this issue. But it would be nice knowing how to approach issues where there needs to multiple variants added, but the existing variant is expressed in too broad terms when you do just that. Perhaps all notgeld should have a default catch all variant for ? or something meaning "I have this general design/unspecified variety"

When adding variants, the best thing is to as for all owners to be moved to undetermined. Before we had this option indeed quite often the original yearline was marked as ? or even worse users were left on a variant without having checked with them (eg a lot of Finnish notes where later signatures were added).

So indeed make all new variant lines, put a comment in the original yearline and ask master referees to move those owners to undetermined and remove that old line.