Hi, I don't know if you count "The cabin in the woods" as part of the slasherverse because of the "deadites" written on the whiteboard, but when Sitterson and Hadley discuss their success rates, they say: "please, we haven't had a glitch since '98."
And what horror movie, which fits the necessary trope format, came out in 1998? That's right, the weird school alien invasion movie with Elijah Wood: The Faculty.
Also set in the US, the movie can be considered the failure in their system since none of the kids die, their procedure failing to collect the correct sacrifices from The Fool (Stokely), The Athlete (Stan), The Whore (Delilah), The Scholar (Zeke), and The Virgin (Casey). Since they survive due to a homemade drug invented by The Scholar, it also explains Hadley's retort that "in '98, it was the chem department's fault."
Ashleigh Millman did all of this. Or at least, I found out about it thanks to her.