I do not believe they know, but they like us are using their best judgement and predicting who they believe might win. That's why you saw Best Book on the telecast this year - they wanted Tina Fey up there. It's usually only Book and Score that fluctuate between on and off telecast recently.
"Oh look at the time, three more intelligent plays just closed and THE ADDAMS FAMILY made another million dollars" -Jackie Hoffman, Broadway.com Audience Awards