Hi Mahesh!

If a student accepts a seat in an NIT in 1st round and after that in later round he or she gets a seat in an IIT, then that candidate is expected to report in the reporting centers of IITs for document verification. Also, if a student accepts a seat in an IIT in 1st round and then in later round that person gets seat in NIT, then again that candidate needs to report at NIT reporting centre. Otherwise, both the seats will be forfeited of that candidate.

I hope it helps. All the best!