Hello Aspirant,

See difference between 2021 and 2031 is of 10 years which is sufficient time to change the rules and implement new rules so at this point of time it is quite difficult to predict whether you OBC certificate issued in 2021 would work for 2021 counselling or not , you can check out the criteria of your state's portal which will clear you that how long the OBC certificate remains valid.

For your reference complete process for registration for JOSAA Counselling is mentioned below :-

• Registration for the counselling on josaa.nic.in
• Choice Filling and Locking of Choices.
• Mock Seat Allotment
• Seat Allotment Result
• Payment of Seat Acceptance Fees and Download of Provisional Seat Allotment Letter
• Reporting to the Reporting Centres
• Confirmation of Admission

Documents which you have to carry to the reporting center for NITs/IIITs/GFTIs :-

• Three Passport Size Photographs identical to the one Uploaded in JEE Main 2021 Registration
• Provisional Seat Allotment Letter
• Candidate Undertaking
• Proof of Fee Payment by e-challan or Internet Banking of SBI for Seat Acceptance (Rs. 15, 000 for SC/ST/PwD candidates and Rs. 35,000 for others)
• JEE Main 2021 Score Card
• JEE Main 2021 Admit Card
• 10th Standard Mark Sheet or Date of Birth Proof
• 12th Standard (or equivalent) Mark Sheet and Pass Certificate
• Photo Identity Card
• Medical Certificate
• Category Certificate (if applicable)
• PwD Certificate (if applicable)
• OCI Certificate or PIO Card (if applicable)
• Print out of Filled Choices for Seat Allotment

Documents which you have to carry to the reporting centre for IITs :-

• Provisional Seat Allotment Letter
• Two Passport Size Photographs identical to the one uploaded during JEE Advanced 2021 registration
• Undertaking by the Candidate
• Proof of Seat Acceptance Fee Payment by e-challan or net banking of SBI (Rs. 15, 000 for SC/ST/PwD candidates and Rs. 35,000 for others)
• Valid Photo Identity Card
• JEE Advanced 2021 Admit Card
• Date of Birth Proof (10th Standard Mark Sheet)
• 12th Standard (or equivalent) Mark Sheet and Pass Certificate
• Medical Certificate
• Category Certificate (if applicable)
• Certificate for PwD (if applicable)
• Passport (for foreign nationals) of candidates & parents or OCI Certificate or PIO Card (if applicable)
• DS Certificate (if applicable)
• Registration cum Locked Choices for Seat Allotment

For complete details about JOSSA Counselling process kindly check out the link given below :-

https://engineering.careers360.com/articles/josaa-counselling

I hope this information helps you.

Good Luck!!