I think there was supposed to have been a subway on Bedford Avenue. At Nostrand Avenue on the A line, at the north end of the station there was an overpass and a parttime booth where a transfer to the line was planned. For the last several years the passageway has been used as a storeage room. If it would have been a BMT or an IND route, I don't know. A few months ago I was at the Bedford/Nostrand Ave Station on the G. I didn't see anything at the station that looked like a transfer to another line.
"I am thinking that this post is mostly legend...."
IIRC, people said the same thing about a tunnel on Atlantic Ave in Brooklyn.