I logged back in, then lost internet for a few minutes. Back now.
I was actually going to ask where you "draw the line" between operetta and musicals, and that is most enlightening. For instance, I'd never given any thought in that respect to something as late as The Sound of Music.
Rodgers, like Alan Jay Lerner, had a
penchant for operetta:
Dearest Enemy, Chee-Chee, Oklahoma!, Carousel, Allegro, South Pacific, The King & I, The Sound of Music. It's a piece like
The Most Happy Fella that confuses me, since it bursts with music that makes me want to call it an operetta but I feel it's really an over-abundant musical. Oscar Hammerstein might consider it a "musical play," and that's his code word for operetta.
I always suspected that Bernstein considered Candide a comic operetta because of the demands of the score - musical theatre sopranos never need the ability to sing "Glitter and Be Gay" - and Sondheim realized that
A Little Night Music needed a bit of vocal heft, although he shies away from calling
Sweeney Todd an opera, which I believe it is.