I caught a clever courtesy accidental in a score yesterday.
Usually courtesy accidentals appear because they are reminding you of a barline change you might have missed. For example with a B-natural in the key of E-flat, you might have a courtesy accidental in the following bar.
This courtesy accidental was for an F-natural in the key of Gb major, and the part had sung an F in the previous bar. So why the accidental? The answer was the F# in the tenor part below. And even though it wasn’t strictly necessary, it was clever to include, because the chord was a D7(#9) with the F being the sharp nine (technically and E#). The arranger knew that without the courtesy, a good percentage of conductors were likely to “correct” the “typo” and have the sopranos sing the F# with the tenors – making the chord incorrect. It’s an innocent but likely mistake on the part of a conductor.
As arrangers and composers, it’s our job to notate clearly, yes, but also to anticipate likely interpretation errors and mark the score to help the conductors make accurate interpretations. Especially in vocal jazz, where the harmonies and voicings often look like potential typos that can be “fixed” with a half-step change.
(We won’t talk about the choice to have the last third of the piece in G-flat. I’m going in to hand mark every C-flat for the whole score tomorrow….)