In the computer biz they specify that the IG conductors will originate at the ground busbar where the Grounding Electrode Conductor lands in the service disconnect enclosure and that it radiates to the equipment in a tree fashion from there with no parallel paths. It will be isolated in any intervening distribution panels. Since we never brought the neutral to the computer panels they would use the insulated neutral busbar for the IG. Green reidentification of all of the conductors made it apparent this was a grounding bus. Sometimes they were also labelled that way. Usually we also had a bare wire ground bonding conductor to the enclosures too.