Hey,
The point of the catalog is to list every AMV that was ever released to the public. If a video was released to the public either by entering into a convention contest or made availabe for public download, the video entry should remain in the catalog.
Remasters should be uploaded to the original video spot since the video is exactly the same as the original, frame-for-frame, except for better visual quality (ex., DVD source instead of VHS source). For remasters, simply request for the file to be deleted so that the new one can be uploaded.
If the video is modified (scenes changed), the video is then technically a completely different video since it is not the same as the original. These videos are generally called "remixes". Remixes should have their own indepenant video entry into the catalog since they are technically a different video.
It is difficult to "accidentily" create a video entry and upload a video.

Eventually there will be a "merge" function. This will mainly be used by collaborators who put a video entry into each of their video listings before the collaborators system was developed.
I hope this helps. ^_^
Phade.