especially against someone with access to expensive lawyers.
For the civil cases case it needs be pointed out that actresses can generally also afford expensive lawyers to litigate on their behalf.
And yes, Wood and her friend and (ex?)partner Gore are "imperfect victims", by which I mean there's some evidence that needs evaluated that they coordinated with other accusers prior to the accusations coming out (including possibly coaching or even writing scripts for them), possibly forged the signature of an FBI agent (Manson claims the agent mentioned in that document claims not to have written or signed it), created email accounts to impersonate Manson, you know, that sort of thing. And those are just things mentioned in Manson's suit against Wood and Gore that media got shown some evidence of.
Another one of the accusations that should be trivial to prove or disprove is the one that he made a short film in the 90s that featured an underage girl and included child pornography - Manson claims the girl was 22 at the time. If she can be identified, then how old she was at time of filming is trivial to determine. As opposed to the Heart Shaped Glasses video, where again you have a whole heap of witnesses and possibly even excess footage of the alleged rape. It's just now we have to jump into the whole "just because there were a bunch of witnesses, doesn't mean they aren't all lying because believe women" bit that seems to be the go to.
Again, I fully expect the accusations against him to be a mixed bag - I doubt he did none of them, but certain ones just feel like they should be easy to resolve one way or the other.
At the time the video was released, Manson himself was ambiguous and contradictory about whether it was simulated or not, but refused to concretely deny that it wasn't and, on several occasions, made statements that clearly implied it wasn't. Following Wood's allegations, he has concretely claimed that it was simulated.
He kept it vague when the vagueness was good for his image, and switched to a firm answer years later when one was required. Again, heap of potential witnesses, shouldn't be hard to get more testimony or evidence than her accusation and his denial over this one.
Also, bear in mind that there were certainly multiple takes and cuts in that scene and it's possible the footage used in the final video was indeed simulated, but that doesn't mean the events described by Wood didn't take place.
Yes, there may still exist some unused footage that might be helpful, and also editing staff who may have seen such footage even if it no longer exists.