Transit wants grounded service-change answers to always include the effective date. Which optimization should the team apply?

Transit that wants grounded service-change answers to always include the effective date should prompt-engineer grounded answers so effective dates are mandatory. Riders plan around when a change starts. Grounding documents often contain the date, but models may omit it unless the prompt requires it. Prompt engineering that forces inclusion of the effective date on service-change answers turns optional detail into a required civic field.

Tuning grounding chunking to keep effective dates with service change summaries fails by enforcement: keeping the date with its summary preserves pairing context but still does not require the model to include the date in the answer. Expanding retrieval top-k to surface effective dates for service change passages fails by enforcement: surfacing more relevant passages makes the date available but still does not require the model to include the current effective date. Enabling grounding validation to check effective dates in service change answers fails because validation can only verify a date that appears against the bulletin and cannot force an omitted date to appear; uncertainty should still trigger retrieval escalation or human handoff—not undated publication of a service change.

Exam caveat: for grounded transit service-change answers, effective date is a required field via prompt/contract—not fixed by keeping dates with summaries in chunking, expanding retrieval for service change passages, or enabling grounding validation to check dates. Operational check: update the grounded answer prompt/schema to require effective dates, reject or regenerate undated service-change replies, evaluate a sample of answers after deploy, and confirm dates match the grounding bulletin.