Via Planeblue's interview tracker, 73.2% are remaining by the end of August, 51.3% by the end of September. It's a different metric because it's invites rather than secondary submissions, but I imagine there's a correlation. That's roughly a 1/3 decrease, but it's a month difference and if I had to guess secondary submissions are what, 2-3 weeks delayed behind IIs? If I had to guess, you're probably working at 70-90% effectiveness.