Are changes of quantities stated in the Price List a CE under 60.1.12 (Correction of mistake in the Price List)?
What constitutes a mistake will very much turn on the facts and circumstances surrounding the contract. Presumably the reason a quantity was stated was because the Client didn’t know exactly what was required and was anticipating some variance that they thought it unreasonable for the Contractor to tender a Price.
I’d suggest that a relatively small variance would not constitute a CE however a large one may do. The common law may also offer some protection to the Contractor in the event that the Client has misrepresented what the Contractor tendered for.