The POST Code diagnostics are used to identify issues when the unit hangs during POST. Once the unit has completed this sequence, the BMC is no longer monitoring or executing commands to further diagnose the unit with these LEDs.
Intel offers utilities to monitor your system once the POST sequence has completed such as the Intel® Remote Management Module.
Today I updated the firmware on all servers, and the undocumented LED code went away. Also, one of them had been displaying the blinking amber fault LED for a while, with no apparent reason to be found in the BMC interface - that went away too.
The only thing that's not 100% clear to me is whether I should have updated the FRU/SDR firmware (from the current D.08 to 1.13 in the downloaded firmware archive) - since it wasn't checked by default in the IDA update tool, I chose not to.