Certified pre-owned - old tires?

in 2023 I bought a certified pre-owned CX-5 from a Mazda dealer. The last few months one tire has developed a slow leak. I’ll air the tires up and about a month later I’ll need to do it again. I stopped by Discount Tire tonight for air since the local gas station compressor is broken. I’ve always liked Discount Tire. They found a nail, said they could fix it for free, and then when they take the tire off they find 2 old rope plugs which they say are unsafe. Since I probably would have needed new tires in a year or so, I just bit the bullet and got new tires.

But what is the official standard for certifying a vehicle? I’ve never had a leak repaired on this car’s tires. So the tires came from the dealer like this. Did I get scammed by them or is this something they wouldn’t check for?