Berenice Abbott took that photo of a block of Union Square West in 1938 for her “Changing New York” project. The two tall buildings on the left – the Bank of the Metropolis at 31 Union Square West and the Decker Building at 33 – are reasonably famous as small but architecturally-significant early skyscrapers. The building on the far right, the Hartford Building at 41 Union Square West, is similar but less famous because it’s architecturally less interesting. The three small buildings between are obviously older.
Both 31 and 41 are L-shaped in plan, so that the back wing runs parallel to the front facade. What looks like two tall buildings mid-block behind this group is actually the back wings of 31 and 41. At Hartford, someone was nice enough to paint the name of the building on the side facade of the back wing to make it really obvious. A map makes it clearer:
Note the side facades of Decker, the rear wing of Bank of the Metropolis, and the rear wing of Hartford. They are absolutely plain brick, as unornamented as anything held up as an example by modernists. The street facades were for show, the side facades – which at any time could be covered by a new neighboring building – were not.