Please refer to section 2.11 thru 2.11.4 on page 81 and 82
and section 126.96.36.199 on page 72 of the technical specification:
I cannot see why your ATX12V v2.0 should not work, unless it is faulty. I would certainly try another power supply.
I've never seen that manual before. Upon reading and reflection, I'd say you are right.
I believe the 24-pin connector was first defined in the ATX12V 2.0 standard, and is the same standard that removed the -5V pin. Since the motherboard supports the 24-pin connector, it is logical to assume it supports this standard even though it doesn't explicitly say so.
Table 31 in that guide also says pin 20 is not connected, which is even more evidence.
At least now I know a new supply purchase will work should my current ATX12V v1.x fail. I'll hold onto the other supply a little while longer to test in another machine should I come across one
Thanks for your assistance.