The clearly in score is the score if the last student to get in last year.
Basically, for regular courses (without folios, umats, etc), they just go down the list until they fill all the places.
Applicants for Bachelor of Awesome
Student A 99.95
Student B 95.65
......
500 places later
Student ZAA 75.50
And they've filled all 500 available places.
Another way of putting it is what swarley said, every applicant with a score above that got an offer.
Obviously, they adjust for SEAS and things like that too (depending on severity and other schemes the university has as well).
So, they don't start with a clearly in. You are provided last years as a guide only.
They don't pick a clearly in of 79.95 out of a hat and let everyone in above that. They would either have too many students (and not enough places) or not enough students, depending on how many people apply.
The clearly in is only generated once they've given everyone a place that year, then, they can see what was the lowest score that got one of their 500 applicants (or whatever) in.
Usually it doesn't fluctuate much from year to year. Your course of 25 (what the hell is it? It's so tiny), might fluctuate a bit since its so small. Usually the wants and perceptions of students are similar from year to year, so, the applicants are roughly similar. Sometimes dramatic jumps or falls can occur (for instance if someone opens up another pharmacy or medicine course or something) but usually, its fairly similar.