Correcting arithmetical errors in Bills of Quantities NEC4 Option B

If a Contractor makes an arithmetical error when revising a bill of quantities for a compensation event by incorrectly extending the Quantity and Rate resulting to total being less than is should be, who holds the risk to correct this error?
I’m assuming this would be held by the Contractor even if the Project Manager accepts the quotation without spotting the error?

The risk lies with the Contractor once the compenasation event is implemented.