If for collecting purposes, without a doubt era-specific vinyls are more highly valued. If we are talking about audio quality, provided they were not recorded with digital equipment, remakes of old vinyls should be perfectly identical to the dated ones. Usually, labels hold onto the master, from which all copies are made. The master is obtained via chemical means and is indelible. Unless it is treated really badly, it is practically eternal as it is made of an alloy of tin chloride, silver, and nickel. By always copying this disc, it is possible to always have faithful copies just like those from the era, which always came from the same master.
Here you can find the process... From the creation of the master to the copy.
http://www.youtube.com/watch?v=JqvxjBSmNN4
