Since I'm more like a "manga version" DB fan, when I say DB I think about the DB and the Z as well, sorry for the inaccuracy. For me it's one continuous storyline. The Z brand was just a "marketing trick" for the new series, they didn't even have a break between the the 2 series' broadcasting (or making) in Japan.

I don't know much about the american releases, I have seen a few of them and all they did is that they resized and cropped the videos to HD dimensions + did some awful contrast/lighting/colour correction + censored some scenes. The best release so far is the Japanese Dragon Box in 4:3 standard dimensions with a really really bad audio quality.

I remembered wrongly about the 16mm prints. They have them, it's just in a bad condition. That's why they should re-record the whole thing with the original celluloid and background images. But that's not possible since those are already fan properties. Even u could buy them on the Ebay.

The audio was the one that lost, sorry for the confusion. They were recorded on separated rolls but later on they mixed those with the video on another tape and threw the original away (they said it took too much space...). It resulted in a really low volume and bad audio quality. There are rumors that some non-Japanese TV studios still have a copy of the original audio rolls (they got it for the translation/dubbing process).