It need a while for me to unterstand how it works , but this is the way:
If you use Pin 17 for + and Pin 1 for - of the LED , this will be display 1 LED A.
Pin 17 + and Pin 2 - is LED B , Pin 17+ and Pin 3 - is LED C and so on , the last one on this group is LED "DP" , where you have to use Pin 17 for + and Pin 8 for - .

I will give you a few examples to understand the other LED groups:
19 + / 1 - is Display 3 LED A
20 + / 3 - is Display 4 LED C
and so on.....

Just look here and think about it some minutes....
http://www.symprojects.com/dlc-247-configuration/Best regards,
Martin