Seeing as how YouTube limits a single live stream session to 12 hours, it wouldn't surprise me if Amy/Dave/Millet Sports didn't actually record all 7x24 video. The live stream was done with an iPhone mounted to a tripod and when the 12 hour limit comes up it stops and Dave Keighley would have needed to notice and start a new stream. Most likely what happens is that he doesn't notice for a few hours, which is why we have those big gaps in the live stream videos for Sept. 6 and Sept. 7 after the initial 12 hour stream. It kind of makes sense why they would be so reluctant to share the video because they do not in fact have 7x24 coverage like they do prominently claim.
I think you hit the nail on the head. There are probably no tapes to be found.
Besides, why would they (or Dave, if you insist Amy is innocent) record 24x7 if he knows they're not anywhere close to the record. It only makes sense to preserve the effort if you're going to use it to prove your case. If you know you aren't going to make it, there's no sense recording incriminating evidence that could be used against you.