The traditional Broadway overture was a suite based on 4-6 of the show's potential pop tunes.
Usually late in the rehearsals the composer, director and a few others would try and pick the possible hits or which songs would work best in orchestral form. The orchestrator would then fashion a 5 minute suite. If a song was cut in try-outs it would have to be edited from the overture. And sometimes a hit song emerged after opening night and was inserted into the Overture later. (Richard Rodgers had "I enjoy being a girl" added to the FLOWER DRUM SONG overture.)
In the 1960s and 70s, as the split began between popular music and theatre music, more shows began with an opening number: "Willkommen", "Aquarius", "Company", "I Hope I get it" etc. and in a way trained audiences to expect a cold start.
Even in regional and community theatres I have noticed that many people believe the Overture is just background music for their conversations. (They also sometimes feel the same way about the show but that's another matter.) In fact that led to the decision to cut the Overture to THE PRODUCERS down to a 30-second prelude. Now, if ever a musical comedy needs a traditional Overture it is that show. (The full Overture is on the cast album.)
There is a difference between an Overture and a prelude. A prelude is usually short thematic statement, so I tend to think of PHANTOM, CATS and most ALW shows as having preludes. I also consider DRS and PIAZZA's opening music to be more like preludes.
CAROUSEL does not have an Overture...The Carousel Waltz accompanies a staged pantomime.
How is the new Overture for PAJAMA GAME? The original has always been one of my favourites.
Cast albums are NOT "soundtracks."
Live theatre does not use a "soundtrack." If it did, it wouldn't be live theatre!
I host a weekly one-hour radio program featuring cast album selections as well as songs by cabaret, jazz and theatre artists. The program, FRONT ROW CENTRE is heard Sundays 9 to 10 am and also Saturdays from 8 to 9 am (eastern times) on www.proudfm.com