Musical

[pdxdjazz]

easier to think of it in terms of the initial key, rather than a subsequent one.

I agree. Lots of tunes have actual key changes (either integral or arranged). Mack The Knife and Fever come to mind. Set the key where it starts. If desired, add a text note "KEY CHANGE- up -3rd” or some such.
If you state an actual key in text, eg. Eb, it won't transpose along with the chart.
You might add "KEY CHANGE TO" in text, raise it above the line, then add the new key as an alternate chord, that would permit easy transposition of the chart.

If the song starts with a ii-V-I, don't label the key as ii. It still should be I. Remember, some tunes may start on the IV.
Some tunes start way out in left field and then wander all around taking the long way home. In that case, I'd select "home" as the chart's key. That would help my "gps" when playing it.
.
In sheet music the key signature is necessary to facilitate reading/playing the notation.
In iRp the song's set-key should be an easy way to get everyone on the same page rather than an exercise in musical correctness.
That said, when the pianist signals "two fingers down" I'm gonna be ready for Bb/G-.
Please take care when signaling G/E-....
)BOB