There is. As Nameless said, the pinouts on a 16 port SLI card is two pairs, skip a pair throughout the block. So pin 17 is port 12.

PINS PORT
1,2 1,2
4,5 3,4
7,8 5,6
10,11 7,8
13,14 9,10
16,17 11,12
19,20 13,14
22,23 15,16

Carl, remembering why I hate iDCS... and formatting in this post