I found Spikestuff uploaded some movies to Nicovideo, and some nicovideo users regarded them as just a redistribution but not as TASVideos' official upload. That's probably because some movies on the site have already been uploaded by their authors, and other ones by volunteers. Some users don't read description (or even cannot read English).
Let me suggest some tips on uploading videos to nicovideo, in order for you to avoid such confusion.
Japanese description
Most users of Nicovideo are Japanese, so Japanese description is the most suitable for Nicovideo uploads though I'm not sure what purpose Nicovideo mirrors are uploaded for. I think just one sentence, such as "この動画は TASVideos による公式のミラーです。", would be enough to make no confusion (this means "this is an official mirror by TASVideos").
Tag management
Everyone can attach tags to a video, and an uploader can lock a few of those tags attached to his video. Tags play a role of great importance in Nicovideo, so setting accurate tags would make contents of the video much clearer. Recommended tags which I think should be locked are the following.
- ゲーム, which means "game". This can be set as a category tag, and most TAS videos on Nicovideo are categorized in the ゲーム category. I do recommend you doing so.
- TAS.
- TASVideos: hopefully this will explain that the video is officially uploaded by TASvideos staff. TASVideos is still unfamiliar to most of those people who even watch TASes, though.
- The game's name. In my opinion, the Japanese title is better to use.
These two points are somewhat cultural. There is also restriction on filesize, bitrate etc., but I can't explain it well in English, so I leave it to someone more experienced.
I hope it will help you. Any suggestions are welcome. Thanks.