For example on mapping pins without probing. Notice which pins have the full oval and which have the open cross-hair:
This is the bottom of the receptacle socket in the Logic Board that the CPU Riser Card plugs into. Sanded down to a ground plane (or power or signal that is taking over nearly the entire layer other than VIAs, but probably ground). The solid copper is all connected together. Copper pours into the cross-hairs making all ovals with cross-hairs share the same electrical connection (every pair of cross-hair ovals will pass the continuity test).
There are at least 53 cross-hair ovals here. We can group them together using the same color coding in the pin-out spreadsheet.
I guess this is the start of documenting the Mac Pro 2013 connector pins.
A reminder that the socket connects 324 pins between the CPU Riser Card and Logic Board not just what is pictured (~164 pins).