Use a shared set of identifiers
Assign stable identifiers to facilities, zones, fixtures, and products. Agree which source owns each field. Keep a mapping when existing systems use different names for the same location or item.
Make freshness visible
Record when each dataset was collected and imported. A current layout joined to old stock data can give misleading results. Set a freshness threshold appropriate to the decision and flag data that falls outside it.
Version the full scenario
Save the layout, data snapshot, rules, and assumptions used in each comparison. Review those versions together. This makes it possible to explain why a result changed and to rerun the same scenario later.