This is what I'm still wondering about despite me wanting to believe it can last indefinitely. I remember reading somewhere on here that someone found information from a military document that SN can last indefinitely, but after searching for it I couldn't find it. Also 2 things. One is that people use the same SN for years or even decades for meat curing. I went on a meat curing forum and one guy said that he had his SN for 20 years without supposedly losing its potency and that's him constantly opening it and closing it again. I don't know but that's what I remember him saying. And two is that SN is essentially a salt and salt can literally last forever especially since the salt we use in our food comes from salt mines that have been buried under the earth for millions if not billions of years.
I would add something else another user said about its expiration date but I forgot what they said, essentially if I remember right it was about that the 3-4 year range was just a marker or something but nothing definite, I could be wrong.
Here's this for reference: https://sanctioned-suicide.net/threads/stop-spreading-misinformation-about-the-storage-of-sn.69105/
Now the the kicker for me is the stuff they added to the SN and if that will affect its potency over time or if there's any unknown factors. I don't know all that much to say either/or so, but I want to believe that it can last longer than it's expiration date.
Here's this post from @ENDOFTIME from that thread debating the OP: "Most all suppliers list shelf life to be anywhere from 3 to +/- 5 years. Presuming purchasers want the information to assess how reliable any particular chemical/reagent will perform based on age, storage, etc. So are we saying this information should be ignored because manufacturers are only interested in selling more products or the information they are providing is based on certain assumptions that do not apply to all purchasers or that the authors of PPH are the true chemical supplier experts? Who should be the trusted purveyor of "accuracy" - particularly when there is a desire for potency and effect. No trying to counter-argue, just asking."