For wide releases since January 2012, the HSX price taken at Friday reset (before box office data has come in for most releases) was on average 70.4% accurate. This is about the same as most tracking and other projections, and often the HSX price will follow the lead of tracking.
One thing about traders' accuracy - we get it wrong by a big margin a lot more than we get it right. Since 2012, the collective wisdom of HSX has been $30 or more off the adjust 17 times, and within a dollar on only nine occasions. I think it's partly groupthink - just like when you look at the different movie predictions, there usually isn't a lot of air between them - and partly because black swan events are more common than we think (like this weekend, which had TCALL overperforming and BURTW underperforming)