You can check out several reports that will provide a record of what happened.
The Process Summary will show the import process date, time and the filename.
The File Update Log shows all the individual item records that were added or modified with a total record count.
You can use the Customer/ Ship-to Maintenance function to change and correct any customer or ship-to records just imported.
You can also use the Table Maintenance function to edit any of the lookup table elements such as salesperson or ship via descriptions.