Just to clarify, disallowed cost relates to assessments of the Price for Work Done to Date and not the assessment of compensation events. Equally disallowed cost is not a function of what has been allowed within the Target Cost. Please see clause 11.2(25) for the definition of disallowed cost.
I think your question is the age old one of is the Contractor correct to include for staff when there is no delay. As you say where there are additional staff mobilised for the CE then they should clearly be included. Where the staff were on site then it is not so clear and will depend on the magnitude of the CE. Where it is significant then arguably the Contractor will incur staff thickening and I suggest that a pragmatic solution should be arrived at. Don’t forget the assessment is adjusting the Target.
I think your question is the age old one of is the Contractor correct to include for staff when there is no delay. As you say where there are additional staff mobilised for the CE then they should clearly be included. Where the staff were on site then it is not so clear and will depend on the magnitude of the CE. Where it is significant then arguably the Contractor will incur staff thickening and I suggest that a pragmatic solution should be arrived at. Don’t forget the assessment is adjusting the Target.