Define the perimeter
Agree source company, entities, books, dates, currencies and required object families. Preserve source reports at the chosen cutoff. Do not assume a connector covers every source module.
Inspect coverage, not just status
Review sync scope, pagination, exceptions and unsupported families. Compare counts and identifiers as well as totals; missing inactive accounts or historical documents may still matter.
Tie out the accounting
Compare opening balances, period activity, trial balance, AP and AR control accounts and aging. Investigate unapplied cash, credits, posting state and currency differences.
Approve the next stage
Keep the original system authoritative during evaluation. A production transition requires acceptance of the remaining exceptions, verified operating workflows and a separate deployment and recovery review.