The QT was one of the casualties of the Chrystie St. connector. Except for occasional reroutes, there has not been a Broadway-Brighton service via tunnel since then. I'm trying to remember if I ever rode on one. I do remember seeing them. The only possibility would have been in July of 1965, from 34th St. to Whitehall St. We were going from the Empire State Building to the Battery to catch the ferry to Liberty Island and would have taken whatever came first, a QT or an RR.
P. S. The R-27/30s originally kept the old BMT titles on their route signs in conjunction with the new route names. In your case, the route sign would say: "QT Broadway-Brighton Local via Tunnel"
I had one of the original pamphlets when the first stage of that connector opened almost 33 years ago. My mother got it for me one day when she went into the city a month before the opening. It has since been lost. What really killed me was that she went to a yarn store in the Bronx on a D train, and said it really moved along CPW. She got to experience a CPW express dash before I did! On R-1/9s!! I was so jealous.:-)