You could see every trace on the board at each layer. A chip like this story talks about would standout. Also at each point on the board you could probe (traces) end to end. It’s complex. Also the is the integery testing .. a machine that has 1000s of needles that pushes down on the top and bottom of the board at each contact point and test the resistance and conductivity end to end. Put something in the board in the path and the numbers come back wrong.
Signal integrity is really important as it can lead to grey failures down the line. It is really important to find them before you stuff the boards with $$ of components that you can not save if the board is bad.
> A chip like this story talks about would standout.
Sure, you could see it, but to know it was wrong you'd have to have a non-compromised board to compare against. Or knowledge of every design and supplier decision, which Supermicro/Apple do not have.
