NEC ECC: Option A - Can the Employer define quantities as this is not an Option B?

The Employer specified to utilize the NEC 3 ECC contract Option A.
The Employer has no site drawings available for the Contractor to do the measurements which need to be priced in the activity schedule and also due to Covid we can not gain access to the site to conduct a site survey.
The Employer indicated Option A sectional completion and in our view the Contractor takes full responsibility to deliver the works according to the Works information.
Is it allowed that the contract remains a Option A when the Employer specifies some of the measurements or should it change to an Option C?

It is allowed, but I would suggest that an option A strategy will either result in very high prices; no-bids or an artificially low bid which will cause all sorts of trouble if you enter into it e.g. arguments, poor quality etc.

As a result, I would look at either an option B or C depending on other circumstances.