Pairing rather than dispersing
The instinct when numbers double is to spread the experienced people thinly so everybody has some coverage. That produces a crew where nobody is genuinely supervised and the method drifts everywhere at once. Pairing works better: each experienced cleaner takes a small group and a defined zone, and the standard in that zone is their responsibility rather than a general aspiration. Ownership of a zone is what converts a general aspiration into an accountable one.
It also gives the additional cleaners somebody to ask. A person working an unfamiliar building with a task list and no one to ask will make reasonable guesses, and reasonable guesses about method are how a standard slips. Having a named person within sight resolves most of those questions in seconds and prevents them becoming habits by the third night. Reasonable guesses about method are precisely how a standard slips during a peak.
