Mass Update not returning the same number of results using the same criteria set on the Saved Search

When creating a Saved Search or Mass Update for Transactions such as Sales Orders, Invoices, Purchase Orders etc... with the same Criteria set, there are times that the number of results in the Saved Search is greater than that of the Mass Update.

When trying to perform a Mass Update, transactions that are already locked (periods that are already closed) will not be included in the Mass Update. This is because transactions with accounting periods that are already closed are no longer editable. To update or include these transactions on the Mass Update, one must Allow Non-G/L Changes to the Accounting Period of that transaction. The Allow Non-G/L Changes option can be found when navigating as Administrator to Setup > Accounting > Manage Accounting Periods.