one of the things about being a keyboard player back in the Dark Ages before cheap/portable digital synths and "electric piano" meant Fender-Rhodes, exclusively, never mind being in high school and thus not being able to afford stuff even if it had been available, was that one was essentially at the mercy of Whatever Was There.

"They have a piano!"
"Yay" (well okay, that was a prerequisite for pretty much anything)
"They just had it tuned"
"double yay"

Get there.
Play a C. Hear a Bb. Uh oh.
Play a D. Hear a C. Oh shit.
"Umm... did you say this was tuned?"
"Oh yes."
Play a C major scale. Hear a perfectly in tune Bb major scale.
"Why is it ...?"
"Old strings. Tuner said he'd break them all if he tried to tune it up to A-440, so it's down a step."

No big deal. Provided one doesn't have a sense of Absolute Pitch.

The one saving grace was the other instrumentalists were trumpet and tenor sax -- both Bb instruments -- and we all read out of the same fakebook, them playing as written and me transposing on the fly.

so, with a Bb piano, all I had to do was play as written myself and everything would work out. Just make my fingers form chords as indicated on the page and not listen to anything I was playing.

It was a long night. Fortunately it was a New Years Eve gig, so after the first hour or so, people were too wasted to care.