Small amounts get shaved off every certificate. Is that just normal?

It is common enough that many contractors budget for it, which is exactly why it persists. But normal is doing a lot of work in that sentence. A pattern of small cuts is one of three things. Honest conservatism: the assessor certifies what the evidence proves, and thin applications leave room for doubt, so the cure is better substantiation, not complaint. Process: a valuation done in a hurry, rolled forward from last month, correcting itself only when someone pushes, so a polite written query each cycle does the correcting. Or policy, a percentage quietly held back everywhere because most subcontractors are too busy or too polite to reconcile line by line, so silence is what it relies on. In every case the response is the same: reconcile each certificate against the application, answer each unjustified cut in writing inside its cycle, and re-present unresolved sums in the next application so the account carries them forward as live. The compounding matters more than any single month: modest shavings across a long job add up to the largest single difference on the final account, and a year of silence is the other side's best exhibit that the shavings were agreed. You do not need heat, you need a paper trail that says, every month, we saw it and we did not agree.

Consider a drylining subcontractor on a fourteen-month job whose certificates run a few per cent light every cycle, each cut small enough to shrug at. Nobody replies; the site relationship is good and nobody wants friction. At the final account the accumulated difference is the biggest number on the table, and the contractor's surveyor opens with the obvious: fourteen certificates, no challenge to any, the account was plainly agreed as it went. Contrast the parallel job where the same subcontractor sends a short reconciliation email each month, three lines naming each cut and disagreeing with two, and re-presents the open sums in each application under a heading that says previously applied for, not agreed. Most months the email changes nothing immediately. But the final account opens from a different place: a live, documented difference to be negotiated rather than a course of dealing to be defended. The monthly emails took minutes; their absence on the first job cost the negotiation before it began.