I have used some even older than than this, but the oldest that I documented
was 3 years and 3 months, and also UNrefrigerated for 2 1/2 months.
https://forum.fudiabetes.org/t/my-insulin-experiment-for-michel-relax-everyone/
In college, I would never refrigerate it, so it would stay unrefrigerated for the entire school year which I guess was about 9 months or so (I knew better than to put things in the fridge with roomates and such…).
I think I have some older than this now. I can use it if you want me to. I really don’t think the expiration means anything.