De- reservation of un filled vaccancies

Since I worked in an educational Institution earlier, I would like to share that in educational institutions an open category candidaten appointed in Reserved post continues for five years on a fixed pay and in the course if a qualified teacher is found suitable for appintment in that category, the services of fixed pay person ends othewise after five years he becomes regular appointee on scale. This is in the Schools.

While in the College, there was a dereservation procedure prescribe where  the reserved post was being advertsed for five years and in case of reserve category candidate not found, the post used to get dereserved and  "Open' for all.

I think there are different rules prescribed for different categories depending on various factors. Like, the signle posts were not to be reserved etc.