I think I've been underpaid
The certificates kept coming in low, and I never had time to check whether their notices were even valid.
What's happening?
On a live job, disputing every certificate is not realistic. You take the payment, note the shortfall, and keep the project moving. By the end of a long contract that habit can leave a lot of money behind. Where a valid application went unanswered by valid notices in time, it can have become the sum legally payable for that cycle, and those cycles can still be checked.
Those rights do not disappear when the cycle ends. They sit in the paperwork you already hold: applications, notices or the absence of them, and payment records, waiting for someone to go back through the file cycle by cycle.
The solution
A systematic pass through the file, cycle by cycle.