Freeze the cutover point
Choose a clear date and time after which movements will be entered into the new system.
Clean product and SKU records first
Opening quantities should map to stable products, variations, units and locations before import.
Count physical stock
Use a controlled stock count rather than blindly importing a legacy balance that may already be inaccurate.
Separate quantity and valuation
Confirm both units and the cost method or opening value required for financial reporting.
Validate a sample before full import
Test representative simple and variable products, multiple locations and unusual units.
Reconcile immediately after migration
Compare imported quantities and value with the approved opening-stock file and investigate every difference.
The operating principle
Every event should remain connected to the product, contact or transaction that created it. That is what lets ERP explain a number instead of only displaying it.