Re: Silly NIC games ...
Du you buy MAC addresses from a global authority, like IP addresses?
Then it sounds like someone bought 20 addresses since they were only shipping up to 20 network cards in one multi-pack.
Or, after manufacturing each 20, something with a counter on the production line got reset.
Or, the manufacturer actually had 40 MAC addresses and you were just unlucky not to get one Box A and one Box B.