Comment by bell-cot

> I still wonder how...

A 500 lbs bomb falling from altitude can bury itself a fair ways in soil. Most of its fellow bombs will have good fuses - and with the mess they make, it would take some careful excavation in just the right spot to find the dud bomb. (Or, maybe it fell in a patch of overgrown brush in a park, or in a river, or a farmer's pond, or ...)

And with the scale at which Germany was bombed in WWII, there was nothing remotely resembling the resources to carefully excavate all the myriad square miles where dud bombs might have fallen. Either during the war, or after.