Could be they are production over runs from the war era or they could have been made during the 50's or whenever they rebuilt the guns. Another good site is
www.7.62x54r.net, but if you have Yahoo home page, they try to block you going there for some reason. I suppose maybe there is a specific indicator like color of the sling if it is not dated(guessing) or some other detail but if there is no date on the sling(if they are dated) all you can say is that it is an authentic Soviet sling for the MN. I treat the dried looking leather parts on them to soften the leather and prevent cracking. And it looks better.