Content Categories + Responsive - any solutions?

Thank you.

I've created Filters to correspond with my existing conditional tags.  Is there a way to allow more than one conditional tag per filter?  I'm not talking about sub-categories or sub-filters.  I have a tangled web of conditional tags that I'm now trying to simplify, for example,

Tag1 =  content A

Tag 2  = content B

Tag 3 = contentAandB

Tag 4 = content C

Tag 3 represents information that is shared between both, but excluded from content C.

So for the filters I would like:

Filter A  = content A + contentAandB

Filter B = content B + contentAandB

Filter C = content C

This doesn't seem possible.  So, I went back and removed the "contentAandB" tags everywhere and replaced them with 2 tags, "content A, content B"  at the topic level.  The filter doesn't like this because when I switch filters, the files with 2 tags (A and B) do not display in the correct TOC order....it's like they keep the same TOC level as the previous filter, which is way out of whack with what displays. So, that's not going to work.

The other thing that I tried is to put the "contentAandB" information in a snippet and then create 2 topics...one which would appear in Filter A and one would appear in Filter B.  While this is a headache, in theory I thought this would solve the problem but now its causing problems with my TOC, i.e., a book can only link to one topic, and having 2 identical books won't work because they will both display when no filter is selected. (With webhelp, I had 3 TOCs....so I wasn't thinking of the 1 TOC requirement here and filters...) ech.

RH 2017 13.0.257, Responsive HTML5