PORTOFINO was a flop. POUSSE-CAFE was a flop. CARRIE was a flop. DANCE OF THE VAMPIRES was a flop. All of these shows lost money AND had short runs. That what I consider makes a flop musical. A show NOT returning its investment doesn't necessarily make it a flop.
Take Stephen Sondheim for example. He hasn't had a single profitable Broadway show since A LITTLE NIGHT MUSIC in 1973! Would you consider SWEENEY TODD, SUNDAY IN THE PARK WITH GEORGE, INTO THE WOODS and PASSION flops? In fact, I would say that Sondhein had only two genuine Broadway flops in his career: ANYONE CAN WHISTLE (9 performances in 1964) and MERRILY WE ROLL ALONG (16 performances in 1981).
Praying Decca Broadway will put "Don't Bother Me, I Can't Cope" on CD!