Bring the refusal notice, any related application materials you have and a factual account of subsequent events. Identify missing records explicitly.
Avoid interpreting the notice alone
Ask counsel what the decision means for the proposed route and whether further records are needed. Do not substitute an informal description such as paperwork issue for the actual reason stated. Organising the file supports review but cannot establish that a past matter has expired, been cured or become irrelevant.
Record what is missing as carefully as what is held, and revisit that list as retrieval proceeds. Missing records are the part of the file that changes, and a gap left unstated tends to be filled by a recollection that hardens over time into an assumed fact. Bring the refusal notice, any related application materials you hold and a factual account of subsequent events, marking explicitly what has not been located and who is looking for it.
Ask counsel what the decision means for the proposed route and what further records are needed. Do not substitute an informal description such as a paperwork issue for the reason actually stated in the notice. Agree a date by which the outstanding items will be chased again, and keep chasing.
A located record can also change the answer, so report it promptly.