You have slightly confused two different processes here. If you had reason to believe they might not be providing enough material, you could have notified an early warning. That should have prompted a risk reduction meeting (early warning meeting now under NEC4) to discuss whether that could be an issue and what could be done about it and agree the actions going forward.
As soon as the Contractor KNOWS they have not been issued all of the material they should notify that as a compensation event. The PM would then have to respond within a week if they agree it is a CE or not. If yes they then request the quotation which will include the assessment of any time affects as well.
Your original question is do they have to respond to an early warning. So taking that as a question (As what you have listed here I don’t think was an early warning really) then strictly speaking no they do not have to respond to an early warning. However, they would be pretty stupid not to as discussing it at a meeting could then avoid that problem becoming a problem at all or at least mitigate its effects in someway. The Contractor even has the power to instruct a risk reduction meeting - and if the PM does not attend then they have lost the chance to mitigate the situation.
If a Contractor notifies an early warning, instructs a meeting but the PM ignores both, the risk to the Client is that this may now cause an issue that you cant avoid that may also then be a compensation event which would then cost more money than it might have.