It looks like lawyers have lied? Naaah. They'd never do that.
The lawyers, or rather barristers who appeared in court would care a little too much about their careers and the chance of jail for lying to the court, not worth it for what they get paid for a few jobs (IIRC at least one has already come out and stated that what he gave to the court was all he was told existed and he'd specifically checked).
I can't speak for the lawyers employed in house by the post office who would have been under pressure to keep their long term jobs.
The management on the other hand, definitely, especially if they thought they could get away with claiming they didn't know the law and "didn't think to
ask for specific advice" about the legal requirements to turn over all the documentation including the drafts. Which is how they usually weasel out of it, they know full well what the requirements are but by claiming they were not told they can feign ignorance and get just enough uncertainty/deniability to get away with it.