During the course of this period, it is common for both the authority and private partner (still as preferred bidder or successful proposer) agree on certain minor changes in the contract to resolve mistakes or clarify ambiguities. It may also be necessary to incorporate specific features of the winning bidder's proposal into the contract according to some practices (while in others, the offer is directly considered a part of the contract).
However, in most of the jurisdictions, any material change that would potentially result in another bidder bidding differently (if they knew of the change), is forbidden. This is good practice in terms of PPP strategy and framework. In these cases, the border between a clarification and a change may be subtle and such changes requested by the preferred bidder should be carefully assessed by the procuring authority before it decides whether to agree to them — even at the risk of the contract not being signed and a need for re-tendering.