Shipping history on UPS.com only reflects packages shipped via UPS.com, not via NetSuite. That is, shipments processed from NetSuite aren't visible on UPS.com. Likewise, shipments processed on UPS.com aren't visible in NetSuite's UPS shipping history.
Each UPS account has a cumulative shipping history, regardless of how often it's registered or where (via NetSuite or UPS.com or other solution). The best place for a customer to access their shipping history for a specific UPS account (regardless of shipping system-NetSuite, UPS.com, WorldShip, other 3rd party shipping solution, etc.) is through their UPS bill (online or paper).