A party should use supplemental interrogatories and demands in an efficient and effective manner. They should be sent at least once a year and no later then 90 days before trial. The responses you obtain should direct you on how to proceed with your discovery plan. If the responding party says they don’t have any further information, then you need to solidify that point by either way of a motion to compel further responses, requests for admissions or motion in limine so no further information can be admitted at trial.