Conversions are proposals. Only scripts you select are converted, and nothing is deployed to NetSuite by the app.
Vendor-owned code can't be converted here. Scripts from bundles or SuiteApps are not yours to overwrite, since the publisher's own update would replace your change. They need a 2.1 release from the publisher. They are counted on the dashboard and given a higher risk floor.
Scripts without source are handled cautiously. Scripts with no source can't be analyzed or converted, and they are skipped in bulk runs with an explanation. Their risk scores are not reliable.
Risk is not the same as complexity. Complexity follows Oracle's published scoring factors. Risk also accounts for business criticality, vendor ownership and APIs with no 2.1 equivalent. Scripts with no criticality rating score in the middle, never at zero.
Map/reduce candidates. Scheduled scripts that call nlapiYieldScript are flagged for re-architecture as map/reduce rather than a like-for-like port.
Bundle-installed scripts are not in a default import. See step 2 under "Import your scripts". Locked records can't be imported by any route.
Re-importing updates the catalog. Scripts are matched by script ID, and their deployments are replaced with what the import contains.
Demo instance. If your instance is a demo, a reset control returns the catalog to its seeded state. This also happens automatically each night at 04:00 UTC. The control does not appear on a real instance.