An AIS identity mismatch does not prove spoofing; it indicates data quality issues requiring corroboration to assess vessel identity accurately. AIS static identity fields include MMSI, call sign and name, IMO number, vessel dimensions and ship type; several are set during installation and require amendment when vessel identity or configuration changes. A limit on accuracy exists because received information is only as good as the transmitted data, and faulty input can mislead other vessels.
USCG guidance records that invalid or duplicated MMSIs occur and that reports from vessels using the same MMSI can appear as one target jumping between positions on a graphical display. Official guidance documents identity fields that require updating and invalid or duplicated MMSIs that can confuse target association, so one mismatch can have more than one data-quality explanation and does not establish deliberate spoofing. While conflicting identity data raises questions, it does not by itself prove mistake, intent, or vessel identity without additional evidence.
