I agree, but overselling would mean that even if 20% decided not to come there is still a larger pool of students to fill those seats.
Might not be a great Idea, Making it so you can throw your student tickets up on an app for any other student to get or trade etc might be a better idea.
I can admit when I am wrong. But a student transfer app for tix, set up through the University, so anyone can sell, trade or give away student tix just like they do for general public, just easily transfer to another student ID is probably a better Idea, it would allow other people to go when someone cant or dont want to.