I get generic, store brand, creamy peanut butter. With preservatives it lasts for, well ... I've never sen it deteriorate. It may separate a bit, and the flavor gets bland in the long run, but I've had peanut butter that was stored for ten years in a kitchen cabinet, not refrigerated, and it wasn't bad. Picky eaters might turn up their nose but if you're hungry, in a survival situation, it works.

I suspect that it would still be eatable for years more.

Most of the survival foods, Datrex and MREs, and similar, tend to remain eatable for years after their 'expiration dates'. You lose flavor and, possibly, nutrition but they still swallow and keep the legs pumping.