The answer is that it depends on what the contract says, whether it formally recognises PC Sums (which the standard NEC form doesn't) and how they are to be administered under the contract.
Hopefully there is an additional compensation event added to specifically deal with this issue, otherwise the normal risks under the NEC would continue to apply, including the risk of an amount in the activity schedule not covering the actual cost of that activity. If that is the case then the matter would fall under the share calculation procedure in core clause 5.
Hopefully there is an additional compensation event added to specifically deal with this issue, otherwise the normal risks under the NEC would continue to apply, including the risk of an amount in the activity schedule not covering the actual cost of that activity. If that is the case then the matter would fall under the share calculation procedure in core clause 5.