Date Nails

Great article and interesting history of ties.  One thing I did not see covered was the subject of date nails.

Perhaps it varied by area and railroad, but here in Canada, the ties were labelled with a date nail set into the tie to record when it was laid. The head of the nail had a number (like "44") molded into the metal of the head, to signify that batch of ties was laid in 1944.   I guess as preservatives improved and record keeping got more automated this practice of applying date nails eventually ended.