NEC4 ECC Option A Section 8 Liabilities and Insurance - liabilities not listed as either Client's or Contractor's

Could you please clarify whose liability are events which are not listed in Section 8 as either the Client’s or the Contractor’s? Option X18 Limitation of Liability, has been included in our NEC4 EC contract, but a tender query has been raised, regarding the apparent unlimited liability (and therefore damages), arising from ‘claims from Others’, Clause 81.1 bullet point 1. X18 refers only to Client’s or Contractors liabilities.

My old professor - Prof John Perry who was one of the original NEC co-instigators and hence drafters told me never to allocate some risk to the Employer/Client and some to the Contractor which is exactly the opposite of what the NEC Steering Group have done for NEC4 causing questions like this.

So far, in practice, I have not come across any liability which ‘sits in the middle’ and is not allocated to either Party so at the moment there is a theoretical gap - if that offers any reassurance - but presumably the initial liability would be with the party who is having the claim made against them and as it is by a third party, it would indeed be unlimited.