I finally managed to run a playtest with someone else and it turned out to be incredibly helpful, even only as a partial play-through of the first half of the game. I'd already updated the rules a bit from what's here, but even during the playtest we were chopping and changing mechanics to focus and streamline the game and I've still got more updates to make.
Probably the biggest single change is replacing the interview mechanics in part 2/the shoot with the questions and answers from part 1/setup. It's almost seamless, since both mechanics are just questions and answers with people from different age groups, but it dumps an unwieldy creative burden (the playtest actually stopped dead in its tracks at the first interview) and lets players establish and challenge the backstory/official narrative at the same time.