Intercompany Integration for databases with existing transactions

Hi All

Has anyone implemented intercompany integration (for trading and consolidation) on databases with existing transactions and found any issues? I'm not sure how to prevent old open AP/AR documents created before from synching again or how to manage customer/supplier codes as existing BPs contain transactions. For the consolidation P7L would be OK but what about the balance sheet? Do you have import 10 years data?