They tried that little tune "Shave and a Haircut," but the timing for everyone else to come in didn't work, so it became one note, which is obviously much easier to count off of.
Anyway, going back a bit to this idea of musical cues, none of the clapping you saw -- whether it's during the marching band-like sequence or this clap early in the song that I don't remember really
did happen -- was a cue. Someone brought up Donna Lynne's cue in Sweeney, and there were things comparable to that in Company, but they were much, much more understated -- little nods of the head, or cutoffs by the musicians out of the playing space. Gestural cues amongst musicians can often be very tiny, because a lot of times you can just
feel when it's right. For example, Barbara Walsh would start off the off-stage "Bobby..." part, and then they'd go right in, or Matt Castle would give cues or breaths from the piano, but nothing as noticeable as the Pirelli cue. I think in a way, that was a character choice as well as a practical choice -- if you saw the conceit there as one of, say, music therapy in an asylum, then her position as the sort of maternal doctor made it right for her to start it all off. The Company cues were less direct, if you will.
A work of art is an invitation to love.