NEC4 TSC Option A - How to set total of the prices with unknown quantities

I am currently working with a local authority who is migrating to the NEC suite of contracts. The highways drainage contract will be on an NEC4 TSC Option A but I am unclear as to how the price list should be populated as “expected quantities” are set within this and we have a large amount of unknown quantities at the outset.

In terms of process, we know that there are 100,000 gully pot cleanses that need to be carried out, but this activity will also inform the repair and replacement works that will be required but are unknown until the cleanse has taken place.

There is therefore no way to accurately include an expected quantity for the repair works to build up the total of the prices.

One route I am considering would be to allow the contractor to submit a rate against the unknown items but leave the expected quantity at 0. I can then further into the contract issue a task order for the repair works once we have established the quantities for each item.

Is this the way to go in my case? I would appreciate any input.

Kind regards,