I think Welles would race in a cab from the Sunday matinee at his Mercury Theatre, straight into the studio, and would voice the scripts cold. (Should that be "coaled", or am I getting my sponsor years wrong?)
IIRC, one story was that during the intro, Welles dropped the "script", flutteringly scattering to the floor, in order to get a rise out of the producer, which he did. Welles then calmly pulled the actual script out of his back pocket.
I can see why the producer would freak out, if as I believe those were live broadcasts.
The tip-off for me to pre-recorded OTR shows in general is when they announce that it’s “transcribed.”
I’ve heard that cab story. And I assume you mean BLUE coal...