@dimitris - thanks very much!
I’d used @Devyn_Cairns wonderful script to delete fingerprints before re-adding in another distro, but would never be able to use both distros with fingerprints simultaneously.
Copied /var/lib/fprint (under su) to my expansion drive, copied it into my other distro, and now I can log into my Ubuntu and Fedora using my right index finger.
Easy as pie.