I worked for a company that made a networking product and we managed to build 1,000 units with the same MAC address (we had a big block of assigned addresses) b

I worked for a company that made a networking product and we managed to build 1,000 units with the same MAC address (we had a big block of assigned addresses) because of a miscommunication with the vendor who provided the preprogrammed microcontrollers.. Luckily the MAC was in a rewritable location so it was possible, if a royal pain in the ass, to reprogram them all.