[chrisss]

> linking to and opening an mscz file adds that file to MuseScore Songbook's library first, then opens it in Songbook. 
> Since all these files are already in Songbook's library, this creates a duplicate library entry.
That's a bug in MuseScore Songbook. You'll notice the same behaviour  if you open an MSCZ file from any Android file manager.
It has been discussed in the MuseScore forum: https://musescore.org/en/node/118301

Thanks for the link to the MuseScore forum discussion ... I've noted this duplicate issue / behavior when opening mscz's from any other source too, as you say.

It'd be nice to get that issue sorted one way or another, but in the bigger picture it is for me at least a minor issue.  Having learned of the Smart Button, that eliminates the time-consuming steps  of switching app's and typing in another search.

Again thanks to Mike for a good fix and to you all for pointing out the tools + options.