How long is my helmet good for?
NHRARacer.com - NHRA RULES
NHRA rule book
General Regulations
Section 21 Page 46
It says:
SNELL 2015 expires 1/1/2027
SNELL 2020 expires 1/1/2032
I won't be the best source for some rules. I retired from racing a few years ago and haven't been keeping up with the rules like I use to.