The appropriate timing depends on materiality, the contract and the supporting evidence. Ask the reviewer whether the current record accurately establishes the investment and operating plan, and how the remaining obligation should be explained. Do not label an estimate final simply to meet a preferred filing date.
Define the update that may be needed after closing
Track when the count, settlement and payments are expected, and preserve the actual results as they occur. Review material changes with counsel rather than assuming every adjustment has an identical immigration effect. If the buyer needs to work in the United States, arrange the required authorization independently; signing the acquisition does not provide it.
Decide what would actually change if the filing waited. Where the outstanding item is a small line the parties have already agreed in principle, waiting may add nothing; where it determines how much capital is committed, waiting is the cheaper option. Ask the reviewer to state in writing which facts they regard as unsettled and what evidence would settle each, since that list is more useful than a general instruction to gather more.
Keep a note of every material event after the file is prepared, with its date, so an update can be built from a record rather than from memory. Keep the buyer's own permission to work in the United States on its own track as well, because a closing date is not an authorization date and no clause in a purchase agreement can make it one.