For the transactionLine table, Fivetran uses the lineLastModifiedDate column to track changes. However, based on the issues we’ve observed previously with this table, the limitation lies on the NetSuite side — it doesn’t always expose the records in time for us to sync, even when using the one-hour rollback window.
That said, I’d recommend a feature request to extend the rollback window beyond the current one hour — ideally to a day or more — to help avoid this issue.