I've posted this several times before.
If it's airtight it will be fine, salt doesn't stop becoming salt, it's like morphine expires but I bet if you still took a lethal OD on expired morphine, you're still going to die!
If anything SN will preserve even better than morphine, it's a salt, a preservative.
It always makes me scratch my head when people bring this up, it's like food companies putting a best before date on a product, fine to eat it after but the food companies say 'if you eat it before this date it will taste better'.
I mean, again, that's a poor example as most food will go bad a lot faster than SN.
If I kept my SN well packaged and sealed and it was 50 years old, I could bet a trillion dollars that if I took it, it would still be night night.
By all means, you do you, I get people don't want to take any 'risks' and have their final moments jeopardised but, especially when SN is gaining more and more infamy, I'd hate for it to get banned and then people choose a more painful method of CTB even though they had 'expired' SN in the house but couldn't get a new batch.
If anyone finds themselves in that situation, honestly, the SN will still work. Unless you've kept it in really bad conditions and it's got wet or damp or something like that, I get that, but if it still looks the same as the day you bought it, that shit's still gonna work!