||Racing nitrous contains a number of additional gases, including sulfoxides, in order to both enhance its oxidative properties for racing and to discourage abuse. While nitrous oxide itself should be relatively stable, there is a chance that over time it could react with some of the other gasses in the racing mix to form lord-only-knows-what compounds. Unless you can find an authoritative racing reference that tells you it's ok to use 10 yr old nitrous in a car, it would seem to be a good idea to get the bottle refilled just to be safe.|
While you didn't specifically ask about recreational ingestion of racing nitrous, it's important to know that racing nitrous is NOT recommended for ingestion because of impurities and additional gases present. Although there are reports of bubbling racing nitrous through water or acidic/basic solutions to strip out impurities, we would definitely not recommend doing this, as there will likely still be other gases present.