Tube Question--Signs a tube is brand new

I just received a box of 25 6550 tubes off ebay which were listed a Never used Sovteks from the early 90s. The seller has 10 boxs of 25. He stated that they were NOS and never installed in a unit. I just tested 3/5 of them and they all test in the middle range of "questionable" on my tube tester. I have some older GEs which test "good" so I know my tester is accurate.

Is there something within the tube which indicates if it has been in operation for a period of time? I compared some of my used 6550s and the top and bottom round plates look grayish and identical to the ones which were just sent to me and supposedly new.