Minimal-Context Applicability Qualification for Ship-Regulation Question Answering Under Partial Vessel Context

Incomplete vessel information can still determine whether a ship-regulation provision applies. We formulate Minimal-Context Applicability Qualification (MCAQ) to test applicability over all admissible completions of a partial vessel context under source-validated regulatory semantics. After system-resolvable information and deterministic dependencies have been incorporated, clarification is restricted to user-queryable facts that can change the decision. A confirmatory evaluation used 25 effective applicability boundaries from China Classification Society R001-2025 and 100 matched cases, with semantics and references frozen before model evaluation. Compared with raw-evidence reasoning, a validated structured-semantic representation was associated with higher rule-level discrimination between partial-but-decidable and unresolved contexts: from 60% to 100% for Qwen3-32B-AWQ and from 52% to 84% for gpt-oss-20b, gains of 40 and 32 percentage points. Exact recovery of the formal decision-essential clarification set reached 96% and 80%, respectively. The comparison evaluates a joint change in regulatory and known/unknown vessel-state representation; these gains describe the language-model conditions, whereas the deterministic MCAQ formal reference is evaluated separately. Context incompleteness alone did not determine clarification need. MCAQ provides a formal applicability-assurance layer that complements authoritative evidence retrieval and regulatory interpretation; substantive technical compliance remains a separate assessment.