Majority of the event was in fact not live. Due to an injury of one of the leads from the last dress rehearsal the night before, everything except for the last song was from a recorded rehearsal.
Vanessa Hudgens (Maureen) and Jordan Fisher (Mark) both starred in Grease Live! (2016) as Rizzo and Doody.
Vanessa Hudgens performed in Rent (2010) at Hollywood Bowl as Mimi Marquez.
During the Christmas Bells song while Angel and Collins are looking for coats, one of the ones they reject is Mark's usual maroon and blue sweater.