Driving vision-language models (VLMs) must accurately understand scenes across diverse conditions defined by Operational Design Domains (ODDs), yet verificationremains sparse: many slices are missing, making empirical failure rates unreliable. We propose SLICESCORER, a deterministic scoring rule for missing-slicerecommendation that combines (i) an exposure-based coverage prior to prioritize rare, under-tested regions, and (ii) a neighbor-failure prior that propagatesrisk from similar tested conditions. SLICESCORER is deliberately simple- interpretable, auditable, and conservative- properties essential for safety-criticalvalidation. For stress testing beyond the declared ODD, we embed SLICESCORER within SLICENAV, an LLM-orchestrated verification pipeline where the modelinterprets developer queries to select relevant operators (triage, scoring, acquisition, evaluation) and vocabulary extensions, composing verification workflows whilekeeping all scoring deterministic and auditable. Experiments on three driving VLMs(WiseAD, DriveMM, Cosmos-Reason2-2B) show that SLICENAV surfaceshigh-risk coverage gaps more effectively than prior slice-discovery methods while maintaining diverse recommendations across the condition space. Ablations confirm both scoring components contribute, and qualitative analysis demonstrates end-to-end workflows from developer query to targeted evaluation.