I'd assume almost no one needs this tip! Just me.
Over the years, I used Libby to see which resources used a specific index. Of course, in the Logos4+ series, you can click on a resource's reference box and see the choices. But that's catch-as-catch-can.
It turns out, typing a number into the Text Comparison tool brings up all (maybe some) of the index choices (except Bibles, since per Help, Text Comparison is for Bibles).
And choosing one, automatically groups the participants for you, placing them in the 'resources' slot (and dumping any Bibles you have listed). But simply typing in a Bible reference, brings back your Bibles group. How convenient?
The is quite useful for the KTU series.
On the downside, this might be an accidental, unsupported feature? Help says TC is for Bibles.
The only reason I noticed it, was that normally in Bible reference boxes, a number means change the verse (2 numbers = chapter and verse). But not in system tools, it turns out.
Extra Credit Tip:
The Text Comparison tools shows the indices that can be compared (multiple resources). To see the full list, type into a CitedBy tool, as an example.