Recover data of app not on Play anymore?
Solved. I found a copy Epistle on the web, and installed it using:

adb install 2388.-Epistle_v1.2.1.apk


Now I can see old data again!

Warning: I was aware of the risk that during installation the app may reinitialize its database. If that had happened, then bad luck. The data was comprised of some notes that, while nice to have, would not have been terrible to lose.