Answered: NEC ECC: Option A Substantiation of rates

For compensation events, the change in the Prices = the change in Defined Costs + Fee - see clause 63.1. So original tendered rates do not apply in calculating this change unless the Project Manager and Contractor agree - see  option A clause 63.14.

So unless you agree to use the original tendered rates, the new 'lump sums' are calculated from first principles in accordance with the Shorter Schedule of Cost Components and you should be able to see that substantiation.