Some of the stuff in in MyDocuments\NeroVision\---

Imported video is where you set up under the more button and configuration.

You might do a search for any large files, maybe you would see something. Or, it just uses the original files and keeps instructions on how they are edited, where they are located, and other information in the smaller files. If you want to confirm it is using the original files, try moving one or changing the name to see if NeroVision can still find it.