I suspect that uneven configurations aren't allowed. IIRC, in the die each core has a direct link to the same core on the other CCX, a direct link to the same core on the other dies in the MCM, and a direct link to the same core on the other chip if in a 2P motherboard.
IOW core #13 is the 5th core in the second die, aka the 1st core in the second CCX on the second die. So it would have a direct link to the 1st core in the first CCX on the second die, as well as a link to the 5th core in the other 3 dies as well as a link to the 13th core on the second chip if in 2P.
So it seems quite likely that all 16 CCX's in a 2P server must have the same number of cores.
IOW core #13 is the 5th core in the second die, aka the 1st core in the second CCX on the second die. So it would have a direct link to the 1st core in the first CCX on the second die, as well as a link to the 5th core in the other 3 dies as well as a link to the 13th core on the second chip if in 2P.
So it seems quite likely that all 16 CCX's in a 2P server must have the same number of cores.