If it is a bill omission then the subcontractor is within its rights to request a CE under 60.6 for correction of the BoQ.
Since it is a CE the default assessment is Defined Cost + Fee. The assessment needs to be based on realistic resources and durations/outputs. The fact that this may come to more (or less) then similar bill items is the Employer’s risk since it prepared the bills.
If the omission is due to a change in Works Information eg type A (in the BoQ) changed to type B (not in BoQ) then the assessment of the CE would be the change in Defined Cost + fee between the type B and type A and any increase (or decrease) would be added. The assessment would not be Defined Cost + fee of type B less BoQ rate for type A.
Since it is a CE the default assessment is Defined Cost + Fee. The assessment needs to be based on realistic resources and durations/outputs. The fact that this may come to more (or less) then similar bill items is the Employer’s risk since it prepared the bills.
If the omission is due to a change in Works Information eg type A (in the BoQ) changed to type B (not in BoQ) then the assessment of the CE would be the change in Defined Cost + fee between the type B and type A and any increase (or decrease) would be added. The assessment would not be Defined Cost + fee of type B less BoQ rate for type A.