Non-continuous steel rails were often dated when forged or extruded or whatever the hell they were. The date isn’t stamped into the rail, but is a bas relief, like this one on a siding rail between the old Holston Glass and Holston Distributing buildings in Kingsport. The date is 1920. Trust me.
This is near to the earliest we’ve seen. The Kingsport track, assuming it was laid down within a year or so after it was forged/extruded/whatever, dates to near the time that the city was re-chartered in 1917. I stand there and wonder what the area looked like then. Pretty thin on the ground, I’ll bet.