Wild guess, since I never used Nashville Notation in BIAB or anywhere else:

Your problems occur in the key of C# and D#. In the circle of fifths, C# is 7 sharps but Db is only 5 flats. Most musicians would likely prefer seeing the piece written in Db rather than C#. D# is far worse: either '9' sharps (crazy) for D# or only 3 flats for Eb. Doesn't it make sense the program would choose the enharmonic with fewer accidentals?

Of course, more tests in more keys would show whether my suggestion is correct or not.


BIAB 2026 Win Audiophile. Software: Fender Studio One 8, Swam horns, Acoustica-7, Notion 6, Song Master Pro, Win 11 Home. Hardware: Intel i9, 32 Gb; Presonus Quantom HD8 & Faderport 8, Royer 121, Adam Sub8 & Neumann 120 monitors.