Clarify whether it is needed for the actual timing question and which records must be obtained. Identify professional work and official charges separately.
Focus retrieval on the relevant period
Ask which facts are missing and what sources can establish them. A broad archive search is not automatically necessary, and an expensive summary cannot replace authentic dates. Keep the calculation tied to the applicable rules.
Decide who owns each gap before agreeing a budget for closing it. Some records the applicant can obtain personally and at no cost; some sit with an employer that will release them on request; a few require a formal application to an authority and take as long as that authority takes. A scope written without that split prices everything as professional work.
Ask the adviser which specific periods are actually uncertain and what would resolve each one, then take back the items you can retrieve yourself. Hypothetical example: an applicant asks a former employer's records office for assignment letters covering eight months, and pays for professional time only on the two months no employer can document. Keep the retrieval tied to the period the rules make relevant, since a comprehensive archive search is not automatically necessary and does not make an uncertain date certain.
Fees for professional analysis and any official charges should be identified separately and in writing before the work begins.