At least on the ROW I've walked in the Northwest, some of the wooden ties have the date stamped on the end or the top surface - sometimes. From the concrete ties I've seen - most of them have a "Born on Date" stamped on the tie, [8-01], or something like that.

Since I've seen date nails go back into the 50's in ties still in use - I think maybe the RR's figured out that if the tie looks worn-out regardless of the date it was put it, then they replace it, if it's still good - good. Maybe during the 1910's & 1920's when tie preservation techniques were being perfected it would have been good to know the "shelf life" of a RR tie. In reality, if a tie goes bad, it needs to be replaced regardless of the installation date.

Talk to ya later,
Dale Jones