Arlington wrote:And is it the case that mostly what's missing from the 1970s tunnel sections is the gaps where the stations were supposed to go? (And what did get built were just the concrete tube/box)? At the dawn of the internet (1994) most graphics for SAS showed "here are the sections that have actually been built."Yes, there is a gap from about 105th to 110th street where the 106th Street station is supposed to fit. (I think the 1970s tunnel from 99th to 105th is now used for tail tracks on the line that opened in 2017.)
There is a completed tunnel from about 110 to 120th; in the 1970s there was supposed to be a station called Triboro Plaza around 121st to 123rd Streets (next to the Taino Towers apartments). That station has been cancelled and replaced by the one proposed at 125th and Lexington.