I'm too lazy to dig them up but I'm pretty sure these practices have been proven in court. I want to say the lawsuit against Newline by Peter Jackson did go to court and the court found that Newline did in fact hold money back from Jackson by a rather large amount. But it's been a while and I'm hazy on the details.

Regardless, as we've said, this is already a rather well-known practice so it's not like it has to be proven that much anymore.