How are sharps and flats written in the Nashville Number System? 5♯ or 5♭?
According to Wikipedia:
Accidentals modifying a scale degree are usually written to the left of the number. ♭7 ("flat 7") represents a B♭ major chord in the key of C, or an A♭ major chord in the key of B♭, or an F major chord in the key of G.
Music Theory for Musicians also indicates the accidental comes before the number, though giving only the example of b7.
All other sources consulted, if they addressed accidentals at all, only addressed b7.