I'd load up 20 or so and try them. But if he's taken good care of them they could be fine. I am currently loading ammo with primers I bought in the early to mid 1990's and they are fine -CCI, Win, Fed. A friend gave me some pretty old primers (Rem older than 1990 I think) and they worked fine - put them in practice ammo to be sure it wasn't critical but never had a failure.
Maybe someone else has a better idea and I do appreciate your concerns.
Only primers I've ever had trouble with, I think I had unwittingly gotten a little oil or sizing lube on my fingers while loading.