A few years ago I heard a rumor that there was a test on a rope that was 10 years old. The rope was in its original packaging and had never been used. The rumor was that the rope tested to very nearly what was stated on the labels. So it would seem that as long as a rope is not used, still in it,s original packaging, and it,s been stored properly, the rope should be OK for use. All that said I want to stress that this was a rumor. I never saw any independent or otherwise test results so I can neither confirm nor deny any truth to the rumor.
In regards to the rope in this instance, if I could not establish 100% of the storage history of this rope I would be hesitant to use it. If I knew for certain that the rope has never left its bag and has been stored properly I would at least feel safe using it for top roping.
At the end of the day you have to ask yourself what that little extra bit of confidence in your life,s safety is worth.