It's very possible that the factory swapped a part out without the RasPi guys being aware, but that doesn't actually happen that often - usually they will ask to swap it and send a datasheet, but if they buy an incorrect part the customer isn't going to pay for it, so this isn't so common.

First article inspection is pretty important because you're very likely to get 10,000 units identical to the first one - that's how factory lines are designed to run. Possibly their testing was booting from an SD card and checking a screen picture came up, which would have caught the more tricky issues like BGA soldering problems, but wouldn't have helped a network issue.

"Our mistake was not imagining that the part might have been swapped out for something else."

"It was – but it was done remotely, and we checked that everything was electronically sound, not that the parts were the ones we’d specified! We didn’t check that the network was working until they arrived here (electronically, it should have been fine if the parts were what we’d asked for), and then it took a while to work out what the problem was because we couldn’t imagine that the type of jack specified in the BOM and schematics might have been swapped out. (We found out when Gordon took a pair of pliers to a port in a desperate attempt to find out what was going on…)"

"We received one initial small test batch of boards which did not have these jacks on them; they tested fine. The first production batch had a different jack in place and it was that batch (we test every single thing that comes from the factory) that failed testing."