The Shubert had a separate balcony entrance until 1963 and the Lyceum has one, but they let people in through a pass door now on the way to the mezz. The separate entrances in NY separated the riff-raff, of whom I proudly include myself, in the "peanut gallery" from the tonier clients sitting on the first two levels. They were a class sifter.
Rocky Horror not only ripped out the lower boxes (don't remember exactly why), but took out the orchestra seats too and had tables on that level. Think of the stepped orchestra at Studio 54 for as close a comparison as I can think.
The brains-that-be thought that the Belasco would continue to be a cabaret-type house. (They also thought Rocky Horror would be a big hit like in London, but it closed in about a month.) It wasn't until the original American Buffalo had to move out of the Barrymore and needed a theatre fast that the orchestra seats were put back. This was about 1977.
There is a non-descript door to the right of the box office windows in the lobby. It is my understanding that the stairs behind this door lead up to Belasco's apartment.
"If my life weren't funny, it would just be true. And that would be unacceptable."
--Carrie Fisher