Log the GC's SCO and track which changes got billed

When a dispute gets argued, the change log is where the money is won or lost — and "we executed it" has always been only half the story. The other half is the GC's own paperwork: the Subcontract Change Order they issue against your subcontract.

Every executed change order now has a place for it:

• GC Executed — record the SCO number and date the day the GC's paperwork arrives. It sits alongside your CO record, so the chain reads signed ticket → change event → PCO → CO → the GC's SCO, end to end.
• Billed — flag a CO once its value lands on a pay application, and see at a glance which executed changes are still stranded outside your billing.
• Both live on the Changes tab and export with the CO register CSV.

Your executed COs stay locked exactly as before — these are operational fields on top of the frozen record, not a way around it.