This is a historical flag distinguishing a circuit that has never yet come up, a 'virgin' entry still at 0, from one that has successfully activated at least once, which helps an admin triaging a newly-provisioned circuit that's stuck down determine whether they're looking at an initial-provisioning problem or a circuit that used to work and has since failed. For example, a brand-new PVC still showing cktNotVirgin as 0 after configuration points the admin toward a provisioning error, whereas a value of 1 on a currently-down circuit tells them it worked before and something changed.