The broken rail that led to the F train derailment in Woodside, which injured 19 and forced hundreds of people to evacuate, was installed in February and is being sent for further analysis, a spokesman said.
The MTA is also trying to locate all of the other rails shipped in December by ArcelorMittal, a company that has supplied rails to the MTA for decades, the spokesman said.
It's not immediately clear how many rails were sent in that shipment.
Rails undergo a full inspection process by ArcelorMirral before they are shipped and those results are reviewed by MTA inspectors, who also conduct additional tests on rail samples, according to the spokesman.
It was not clear what the inspection results of that batch were.
Once they're installed, MTA crews inspect the rails twice a week by walking on all 660 miles of track, and a specialized train car performs ultrasonic testing on every line at least once a month.
It was not clear when the section of rail near the site of the derailment was last inspected or the results of that inspection.
Another type of specialized rail car inspects the geometric alignment of track at least every three months, the spokesman said.
The Manhattan-bound F train carrying 1,000 straphangers derailed near the 65th Street station in Woodside, sending six of its eight cars off the rails.
Investigators had not determined what caused the rail to break.