Hello aspirant, hope you are doing good.

So , first thing that you need to know is that preparatory rank in JEE Advanced is not really a true rank because they aren't  providing you a confirm seat in any college. It's the ranks that are vacant after counselling, and some other students get a chance for preparatory courses. In this course, you will be trained for a year in IIT, and then after a year, you will have to appear for an examination, depending on which you will either get a confirm seat in IIT for that year.

Hope this helps you. Good luck!