USCG is aware of the challenges owners and operators face in opting and installing a BWMS in order to keep up with the USCG regulations. Therefore, after considering the interpretation of the ‘next scheduled drydocking’ with regard to 33 CFR 151 Subparts C and D, the Coast Guard provides extra guidance on what constitutes entry into drydock and the end of an extension period.
Generally, many are the vessels that have received an expansion of the ballast water compliance date that was stipulated...
https://safety4sea.com/uscg-information-on-bwms-compliance-date-extensions-and-next-drydocking/