Updates to official ENCs are sequential, and the sequence is unique to each ENC. A standard ECDIS functionality is the verification that all updates in the sequence have been applied. Thus an indication will be given if an update to a specific ENC has been missed and updating is no longer possible until this missed update is added to the sequence.
Verification of the application of updates can be found in the list of updates already applied, which the ECDIS is required to keep. Should all available ENCs show the same date for the latest update, it is likely that they have not been updated regularly, and the distributor should be contacted for verification. Furthermore it is possible to use traditional sources of information, such as Notices to Mariners, to verify updates.
