I don't have Caste Validity, can I get admission in IIT or NIT?
If you belong from any reserved category, and you want avail the admission through your category then you must need the caste certificate for admission in any IIT or NIT, if you don't have the caste certificate during your admission then you can't avail the admission under your category merit, and you will be treated as a general category candidate.
Hope this helps, all the best.