Neither ! This clause is about how changes in the Prices - worked out under 63.1 - are inserted into the existing BoQ - see the opening sentence of 63.13.
What it does lead to, which I think you have picked up on, is a contractual dead-end in that if the work is of the same type and quantity as the BoQ, but done in different circumstances (say a more onerous constraint due to an instruction changing the Works Information) which makes it more expensive, then the contract is not clear about how the new rate is inserted into the BoQ.
What it does lead to, which I think you have picked up on, is a contractual dead-end in that if the work is of the same type and quantity as the BoQ, but done in different circumstances (say a more onerous constraint due to an instruction changing the Works Information) which makes it more expensive, then the contract is not clear about how the new rate is inserted into the BoQ.