Really interesting you should ask, as I could lean the other way (from my photo's angle) and read his music clearly. And I actually thought about that very plan.
As it happened, of the three songs on which I played, one was new to me and so I printed off the piano/vocal sheets, all 14 pages. And I played the bottom line of the piano plan. At rehearsal, our pianist recognized I was doing that, thanked me profusely! She said she'd let me handle those and she focused higher on the keyboard. That worked very well for us both and I think served the song well.
The other two songs on which I played we've done many times before and I had our usual lead sheets, from which I played.
But, to your question, the tuba had his own orchestration of those two songs. I did not connect those dots until this morning. I could well have played that orchestrated music.
In retrospect, I think injecting the slightly different timbre of the bass added texture vs the tubas and trombone. Not, that I'm biased, of course
Great question!
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