Answer
For SEEMP Part III, success is defined by MARPOL Annex VI Regulation 28.
The Core Criterion: The ship achieves an annual Attained Operational CII rating of C or better on its Statement of Compliance (SoC).
The Failure Threshold: If the vessel receives a D rating for 3 consecutive years or an E rating in a single year, the SEEMP is legally deemed unsuccessful. This triggers a mandatory requirement to revise SEEMP Part III and formulate a Plan of Corrective Actions (CAP).