> gives us some information about the DIMMs, but unfortunately with no overlap with the information about the ranks. We eventually resorted to pulling a DIMM out and checking which ranks were still present when doing the grep above

Did they pull out the sticks of memory while the system was running? Can you remove and re-insert a stick and have any chance of the system continuing to operate?

I can easily imagine chips getting fried this way, unless they're specifically designed to handle such cases.