If your bottles were filled or inspected in Sept of 16, then you can race them through Sept 18.
I suspect the NHRA and some other sanctioning bodies require annual inspection, thus yours says certified until Sept 17. Most agents don't go bad sealed in the bottle...
If the only date on the bottle is Sept 17 and you show up for SpeedWeek next year, you better be giving rides in a time machine to the inspectors
But if your bottle says it was filled or inspected in Sep 16 you will be fine.
Keith, you always get 2 Speedweeks from an inspection, and occasionally we get 3 if we forget and need the bottles inspected at the last minute before going racing... Inspect August 17, race 17, 18 and 19, they will expire at the end of Aug 19.... our tags are punched Month and Year.... the day is not on it so you get more than you think.
Our lines are also cleared annually as part of prep.