NEC ECC: Can an accepted cost saving amount be retracted if later found to be incorrect?

We are carrying out an Option A contract. Our Client de-scoped some works and asked for a cost saving. The saving offered was calculated in error and the sum/value that the clients PM has accepted, is substantially more than that of the activities value in the activity schedule.

Is there a clause in the NEC contract which allows the Contractor to retract the quoted clients cost saving (after the clients P.M has accepted the quote) when it is clear that the contractor has made an error?

Should the PM have accepted the quote or does the PM have a responsibility to allow the Contractor to revise the cost saving quote when it has been highlighted that there has been an error?

If this has been agreed and therefore “implemented” then that is it, it is full and final. Only remedy at this point is relying on their good nature (good luck) or going to dispute process which would be adjudication. Even then you would only get any joy if it is a pure arithmetical error rather than a judgement as to what risk should/shouldn’t have been applied.

Think what you would do if it was the other way round (honestly!) If your quote was too high in error and they have implemented it - would you give them money back? What ever your (honest) answer is is probably then the same answer for this question.

Look - sit round the table with them and prove it is a genuine arithmetical error that they can now see and I am sure that (in the spirit of the contract) they would find a way of correcting it.

The more leading question is how did someone not spot the error in the quote before it went over if it is now that big an issue (if that is not too obvious a question)