Since in 2006 it was mentioned that CBS Paramount Television
did some tests of remastering to HD this show it would lead me to believe they did store the original camera negative. and attempted a HD telecine of part of a show from season 1 (originally mastered to 1" analog videotape) and maybe part of the show from season 3 or later (originally mastered to D2 composite digital video tape) along with uprezzing the CGI original effects to HD to see how they would hold up.
From what I recall, those tests were said to merely involve upscaling the SD tapes to see if they could "get away with it". I'd be surprised if they met with any great success.