OBC NON CREAMY LAYER INCOME PERIOD REG:

The notification or communication from recruitment dept.,  stipulates the validity of such an income certificate period.

Every income certificate issued must stipulate such validity period on such an income certificate.

In case of doubts, always apply and get the latest Income certificate from the competent authority.

It is the authority that is empowered to issue such certificate as per laid down norms and your affidavit showing your income sources.

In case of doubts file RTI Application to that authority and seek laid down norms in the form of a certified copy.