I just went to inspect the tyres on my defender that I bought recently. It's fitted with BFGoodrich Mudd Terrain KM3 tyres. Out of the 4 tyres, 3 read "DOT BFWY KM11" and only one has an additional "0718" for the manufacturing week/year at the end. How is this possible, and how can I determine the age of the other tyres?