I've got 2 Goodyear Eagle NCT 2's on the back of my Sapph and I'm sure Goodyear stopped making them before the mid 90's

They are the same as this
Anyone know how old they are likely to be? When I bought the car it had 4 of them on it but 2 were worn on the inside edges. They are still in good condition with no cracks which surprises me given that they must be very old