I am not sure if this is really an error, however I stumbled over this while designing our own cape for the BBB. I was plotting the drill locations for the 2x23 headers from the zip file given in https://github.com/beagleboard/beaglebone-black/archive/master.zip (LATEST PRODUCTION FILES (C))
There are 97 holes for T04 92 for the headers and 5 others. Four are test points for sure and the fifth looks like another test point.
It appears that the location for TP4 is off.
That drill hole would match with TP9 on the Rev C… (your picture is an A5…)
Regards,