Actually test data is very important but doesnt tell you if the tubes are lightly used or not. It is not unusual for there to be up to a 15 to 20% difference in the test readings on NOS tubes of the same type and manufacturer. So you can actually have lightly used tubes which can test higher than true NOS.
As Ralph points out, the tube pins are probably the best indicator of use. However, if the tubes were tested then there can be vertical marks on the pins. Heat marks/discoloration can also be an indication of use. Problem is that the process of manufacture wasnt exactly as we expect today and variations on things like getter flash, clearness of glass, etc are not uncommon.