Not for nothing, Generally, a railroad buys ties from a single supplier, has them shipped to a location where a tie gang is scheduled to work, distributes them over the ROW, then the tie gang inserts them, in place of the old ties. Railroads are built to standards based on tonnage, use, speed and traffic density. The NS would know exactly where the ties in question are installed. Main line railroad lines are inspected on a regular basis. The Inspector is a Foreman, who would know if there is premature wear, and document it.A wooden crosstie, properly treated is good for roughly forty years. Clearly, these ties weren't that old, but aged prematurely ergo, the manufacturer sold them an inferior product.
Not a new occurrence, however. Several sections of the NEC had to be retied prematurely, because of defective concrete crossties, rated for 50 years, worn out in ten years. Union Pacific, another big user of concrete ties had similar issues. PRR/PC used to buy their ties from Koppers at Newport, DE, until the plant closed due to environmental considerations in the mid 1970s. Creosote, an excellent preservative, is considered hazardous, and can burn the skin.
https://en.wikipedia.org/wiki/Creosote
The NS, is quite precise in it's record keeping, and operations. They demand a lot from their employees, and are not an easy place to work. However, they are generally the safest railroad around, and have a collection of Harriman Awards, (for safety), to Prove It. They also employ a group of very talented attorneys. My bet is on the NS.