When there are multiple interludes in an arc, they’re labeled as (for example) 10.x and 10.y. With the exception of a coming arc that has a LOT of interludes that are labeled with .a, .b, etc.
Huh, neat.
I think I’m going to stick with my current system for tagging purposes, but it’s good to hear Wildbow did figure out how he wanted to do it after a while.