With the caveat that I'm sure there are loads of aspects of the court case that weren't even touched on in this dramatic retelling - based on what they showed I don't know whether they did it or not but there's surely no way a jury could be beyond reasonable doubt about it?
1 - the phone call between Diana and Tecwen lasting 8 minutes? that's not enough to set up an elaborate scheme. Unless there were more comms.
2 - what even was the plan supposed to be? They said that there was 'coughing to indicate no' on one question but the other ones, a cough meant 'yes'. Unless it was one cough = yes, two = no? Why did they not ascertain a specific logic to the plan?
3- The lack of coughing at all over several questions in a row where Charles must've just known or guessed the answer. And was his pattern of answering different on these questions? As they pointed out, how would the co-conspirator know what he knew?
4 - Lack of comparison to some baseline level of coughing and answers being given - they touched on that with showing the Judith Keppel tape but surely a fuller analysis would've been useful?
5 - Only the edited tape being evidence, rather than giving several versions from different mic feeds. And the main other prosecution evidence being that people thought it was fishy/weird etc?