First of all, thank you very much for creating Arduino and hosting this community platform. I greatly appreciate you all!
On to the issue... I spent about two days attempting to upload a bootloader via Arduino ISP over SPI from a Nano programmer to a Nano target. I ended up succeeding by being told about the pinout of the ICSP header, which differs from the ICSP pinout located on page 3 of https://content.arduino.cc/assets/Pinout-NANO_latest.pdf
The true pinout of the ICSP header is:
2 4 6 1 3 5
The current schematic available at that link shows us:
5 3 1 6 4 2
I wanted to report this and hope you guys can get it updated, it would most likely help a ton of people out there using Arduino Nanos over ICSP.