Why is it that only the group “collection“ has the include/exclude option? It would be useful in the other groups, too.
I can certainly add an include/exclude option for most filters, but the assigned/unassigned options don't make sense for a number of other things. I don't track whether a difficulty has ever been set, for example.
Keep it simple.
It would be great if you could add include/exclude to a number of filters. Assigned/unassigned additionally would be even better (but less important).
If it causes big additional effort, just leave it. I'm sure we can live without assigned/unassigned for "Difficulty"
What you consider best, Mike. Include/exclude would be sufficient, I think.