Have no idea about the sub pianist - we can only hope. Our pianist will let me know how it's going.
Here's to success!
Working with the regular guy more than once is the only way. Even when I've just subbed on a keyboard book in a pit, I've sat with the regular player at the show - twice in a few cases - and followed everything while recording it. Having the ability to study that recording - and make one's own very clear notes - is priceless. This has resulted in success each time thus far.
BK mentioned the scribblings. My first time doing this, the keyboardist gave me the worst imaginable book ever. His marks and scribblings were USELESS. I used that pit recording to re-notate my own copy of the entire book, even removing pages that were cut (unbelievable), and when I finally played, it was smooth sailing. I am not bragging. This takes work, and I am so grateful I know a few people, one excellent keyboardist in particular, who have taught me these invaluable lessons.