NEC ECC: Option A - Can a Contractor reassess a previously provided quotation before it has been approved by the PM?

We have forecasted costs and EOT for the works and submitted to the PM for approval. The PM kept requesting more information so the CE has not been approved and we have now realised there were some costs missing and our forecast for the EOT has changed. Can we issue a revised quotation?

I see no reason why not. If you submit a revised quote pointing out the original was wrong - the PM will have to consider this as they have to make a correct assessment themselves. I am pretty sure if you realized the original one was too expensive they would be assessing it themselves lower! They will have to consider your revised quote before the make their own one. If they ignore it and assess it lower, then this could end up in adjudication and if your revised quote is a fair assessment you would be likely to win.

I would imagine - and note my words, I am not being definitive - that it would be viewed in the same way as ‘offer and acceptance’ for a contract. The offer stays open until rescinded, which includes replacement by another offer.

Up until that point, your ‘offer’ is open. Note though that - unlike in contract law - the PM has an obligation to assess the quotation in accordance with the contract as an “impartial administrator”. Consequently, due to the extra information supplied, if he or she is aware that it is too low, then he or she should make their own correct assessment.