There are people on here that have done SRO though. Maybe the box office thought you were asking if they were selling SRO at the time you went to them. They start to sell the tickets closer to showtime as that is when it normally sells out.
They definitely do standing room as I've done it all three times I've seen the show. It's $35 and they tend to only sell it if the performances are close to or sold out.
"Anybody that goes to the theater, I think we’re all misfits, so we ended up on stage or in the audience.” --- Patti LuPone.
I literally just bought two tickets and it's 5pm on a Saturday right now. No one else was in the lobby at the time so I guess it doesn't attract a lot of attention (compared to Waitress where four hours ahead doesn't cut it).