We are currently working on a JV project which has clause X1 included in the contract documentation. We are aware that indices should be written into contract data part 1 but this has been overlooked, What is the best way to progress considering there is no information included within the contract?
From what you say, it is clear that price adjustment for inflation is part of the contract.
So choose an indices that you like and propose it to the PM / Employer. See what they come back with !