While researching another post, I came across this unusual map from 1881:
From Community Heritage Maps
You can see the Stuyvesant Street running on the diagonal from the lower left to the upper right. But the upper right portion crosses the blocks between Avenue A and Second Avenue:
Of course this eastern portion does not exist, and I couldn't find any evidence that it ever did. The street seems to be drawn as a phantom, passing through existing lots. I found a similar routing of Stuyvesant Street on the 1834 Fireman's Guide map, where it seems to end abruptly near the river:
1834 Fireman's Guide
So I wondered whether there is any remnant of this route on the existing grid. A quick check of Google Maps showed me a curiously positioned building. Note Stuyvesant Street to the left and the unusual building to the right:
And zooming in to the block between 1st Avenue and Avenue A, 12th and 13th Streets:
It's very a unusual placement for a building in the middle of the block, and seems less than coincidental since it falls right on the line of the phantom Stuyvesant Street. The mystery continues...
An anonymous poster provided the address of the building, which allowed me to lookup the tax map. Although recently constructed (according to the poster), the building appears situated to maximize its use of the lot. Still may mean absolutely nothing, but that lot shape sure is odd!