As you rightly state, NEC contracts provide for reasonable recompense for changes (compensation events) so I don't see how the principle of Quantum Meruit would apply.
The administration of such a large number of CE's could be made easier and more streamlined if you were to agree percentages for certain items, such as supervision and management.
Furthermore, perhaps deal with programme issues on a periodic basis, such as weekly, an issue which Glenn Hide can expertly advise on further.
Disruption appears to be the difficult issue to assess. Disrupted progress can be compared with the Accepted Programme (or agreed baseline programme), which is hopefully detailed enough to do this. However, an assessment will need to be allocated against specific CE's, presumably the one's you agree to allocate any assessed time against.
The administration of such a large number of CE's could be made easier and more streamlined if you were to agree percentages for certain items, such as supervision and management.
Furthermore, perhaps deal with programme issues on a periodic basis, such as weekly, an issue which Glenn Hide can expertly advise on further.
Disruption appears to be the difficult issue to assess. Disrupted progress can be compared with the Accepted Programme (or agreed baseline programme), which is hopefully detailed enough to do this. However, an assessment will need to be allocated against specific CE's, presumably the one's you agree to allocate any assessed time against.