Currently Airing Anime

Another Episode 7: Okay episode, some more info and lays down the rest of the plot for the series. Preview looks like filler.

Can someone help me understand/clarify exactly how all the 'rules' work?

 Spoiler

- When it started 26 years ago, there were X desks but X+1 kids for the class, which no one could figure out why
- Some times the calamity doesn't happen, but once it starts, it finishes except for that 1 year that his mom was in
- The calamity has a 50% chance of occurring if they pretend a student doesn't exist. Otherwise it will happen 100%
- Every year no matter what, there is always X+1 students for the class because a "dead" student inserts themselves into the class
- The school records show X+1 students enrolled in the class but later they mysteriously change to X students
- The "dead" student is listed as "deceased" once the records are updated. Prior to that, they are mixed into the regular roster
- Students that die that year from the calamity are crossed out in red

The school records part is the thing I need clarified the most.