Age of Lionel 031 Tube Track

I recently received a misc. lot of 031 tube track.  Upon inspection I found that there were differences in the markings on the track.  All said Lionel NY on the ties but there were various markings on the rails: Lionel, Lionel NY, no markings, and various levels of vertical striping.  Does any know how to date the track based on these markings?  I apologive if this have been covered in other posts but I could not find anything in the search.

Thanks!