The ISF must be amended if there is a change or if more accurate information becomes available before the goods enter the limits of the port of first arrival in the United States.

However, if the flexible filing option (FR, FT, or FX) is used, the ISF must be updated with the correct or more accurate information as soon as it is known, but in any event, no 9 later than 24 hours prior to arrival of the vessel in the first U.S. port. If better information does not become available and/or the original information is the best information, the ISF must still be completed using the CT amendment code.