Perhaps I'll start.
When a government contract goes out to tender, it is required to outline the full scope of the requirement, including, as you mentioned, option years. It is not a requirement to exercise those option years, but they are available to mitigate risk for the government in the event that there is a need to no longer continue the services or to address other matters that may arise in the contract.
Without getting into the specifics, because I have not seen the contract or the requirement you mentioned, there may be a number of provisions in the contract that expand the scope or require additional resources, which may increase the overall value of the contract. Without getting into the specifics of the contract or seeing the details, I wouldn't be able to particularly answer that question, but perhaps I'll turn to Mollie to expand on it.