I think you can largely consider shows like Ragtime and Sweeney Todd as sung-through because an enormous amount of those shows is sung rather than spoken. They rely much more on song than dialogue. I tend to think of the sung-throughs as "mega-musicals". If were saying any dialogue excludes a show from being deemed as sung-through, then it would be difficult to name any show as sung-through. Even Caroline, or Change has a small amount of dialogue.
La Boheme is an opera that played on Broadway, not a musical! Just wanted to clarify.
"What the hell happened to you? You look like a Make-A-Wish Kid. You know, I just knew you were gonna bring shame on this new family of ours, and it just figures you had to go make yourself over into some heroin-shootin skate board chic on the only day E! could interview you!" - Cherry Cherry, on her daughter Mary Cherry