According to a listing we found in the American Architect and Building News, the row was built in 1892 by owner/builder Julius Anderson, and architect Lewis Anderson:
"Building Intelligence; Houses; Brooklyn, N. Y.," AABN vol. 36, no. 858 (Jun. 4, 1892): p. 3.
– "Third St., n s, 29' e Seventh Ave., 4 three-st’y brick dwells., tin roofs; cost, $6,000 each; owner and builder, Julius Anderson; architect, Lewis Anderson."
This listing conforms to the historic district's Designation Report, which also credits this row to Anderson & Anderson:
As noted in the Designation Report, however, only #509 is within the current Historic District. The other three houses, closest to 7th Avenue, are not. Can you guess why? Careful readers of this blog will recall how, south of Union Street, the historic district never approaches closer than 100' to 7th Avenue, even if that boundary splits rows of identical houses, as here.
100' is of course the depth of a standard NYC building lot. The boundary of the 1973 Park Slope Historic District seems to anticipate that everything standing in 7th Avenue were ultimately to be bulldozed. In other words, buildings seem not to have been included in the original historic district based solely on merit, but rather on arbitrary extraneous factors including development potential... a highly questionable approach to landmarking, it seems to us.