They're not duds

I've now tested all five of the motherboards (I hooked up a PSU, monitor, keyboard, mouse and debian on a usb stick) and they all work fine. All five booted into Debian without issue. I was a little confused when I noticed the BIOS showed not the 1024mb I was expecting but only 895mb of available memory. But a little research revealed that the rest of the memory had been grabbed by the on-board graphics displaying the BIOS.