When you import statements via the Import Accounts section, the date you select when importing will determine the period in which that statement is included. This is because platforms can differ greatly in their reporting, and the sales included in their reports may not necessarily be for the corresponding month of the statement.
If the import date of the statement is within the statement period you’ve run and you still think it is missing sales, it may be that those sales haven't been reported to us yet.
For example, your sales statement from ampsuite for September, may contain sales from August, July, June, May etc, depending on how regularly the stores account to us.