This problem does not arise with the AP; the exams are sealed
until given. There are other techniques for maintaining the validity of
an exam, such as individualizing the numerical values in the problems by
using random entries for each exam (given on the net). This technique
would not apply to exams that ask questions like: Which vehicle moves
faster?
I'm not so sure that randomizing numbers, "individualizing the numerical values" maintains the validity in the sense indicated above. In an ideal world, i.e. one with algebra savvy students, this would do close to nothing to maintaining the validity. Sadly we are far from an ideal world; so there probably is some rationale towards this method of maintaining the said validity. Naturally, IMNSHO.