Well, they're three iterations of the (B) line
First Generation B line (created in the early 2000s): I believe this was from 34 St Herald Square to Bedford Park Blvd in the Bronx. This reflected suwbay service duringthe Manhattan Bridge closures
Second Generation B line (2007? I think? Not sure): Bedford Park Blvd to Grand Street
Fourth Generation B line (the current version): Norwood to Brighton Beach
I don't recall anyone having made the B line via West End, but whenever the devs decide to release the D via CPW Local to Coney Island, then I guess you can basically treat it as the B line.