I have date nails from the following railroads:
Lehigh Valley 1917 (Moravia, NY-Auburn, NY) Branch. I only have 2 date nails.
New York Central as well as some New York New Haven & Hartford nails with the following dates: 1925, 1927, 1930, 1931, 1933, 1935, 1936, 1938, and 1939. In all I have about 30 date nails.
Most of the info that you are looking for on the replacement of ties can be found in a Railroad Maintaince Program Book. On occation a stray Conrail one pop's up on e-bay. These books tell you every thing about the divition in which the book covers. info in these books tells you things such as:
*# of ties in a section
*year rail bed was undercut
*year rail was last grinded
*location of underground utilitys (public & priviate as well as R.R.)
*Location and M.P. number location for signals, grade crossings and bridges.