There is no conflict between 250.6 and 680.26.

You are still supposed to separate the neutral from the EGC anywhere on the load side of the service disconnect so you should not have any circuit current in the EGC.

Any current you see in the EGC is going to be between separate services and technically it will be on the line side of the EGCs. We tend to deny that exists and it is not in the scope of the NEC.
I had a big dust up with an FPL guy one day when he said there was no current flowing through the earth from their wye distribution services. He simply did not understand the idea that current takes ALL paths. I showed him there was an amp or two flowing in the ground wires running down his poles and he still denied that was current flowing through the earth.
This one had almost 3 amps

[Linked Image from gfretwell.com]

Greg Fretwell