About a year ago, my son in Arizona was between insurance coverages and bought about 2 vials of insulin off of Craig’s list. He met an elderly couple in a parking lot with unopened boxes. Never had a problem.
I regularly buy Guardian sensors from Amazon and E-Bay. They are listed as for research only, but they have always performed properly.
It could have belong to a family member who has passed away or it could be that the person is no longer on that particular medication for whatever reason (like they started on an insulin pump).
Another very plausible thing is that they get their insulin from their mail orders and have their prescription on automatic refill. When a prescription is on automatic refill, the mail order will often send 90 day supply every two months or so. Medication begins to stock pile and, at some point, it can get to the point that you can’t use it all before it expires.