Look at the date of manufacturer stamped on the bottle. If it's too old, the testing site might not even test the bottle because of risk of bursting.
Chances are your bottles will pass the test, but won't won't be recertified because the bottles are past their lifespan. But, the lifespan of the bottle depends on the material the bottled is made from.
Some bottles have an unlimited lifespan. These are things to think about.

Here is a link about testing nitrous bottles

http://nitroustech.com/crown-markings/