I just finished my Certificate Verification for IIT. Should we go for verification after every round or is the first time enough?

Hey Student !
Certificate Verification procedure is required for just one time itself. There's no need to verify the documents every time after each and every Round.
Henceforth, you can take admission in the alloted college and wait to see if the upgradation lies in your favour or not.
Either way, it won't be required to verify the documents every time.

Hope this helps.

Good Luck!