To avail a category benefit  you need to present a NC-OBC national certificate. The authority issuing the certificate must have to mention the details of Resolution of government of India, in which the caste of the candidate is mentioned as OBC.

Your category must not belong to the state directory. All the IIMs have a register in which castes (authenticated state wise as per central norms) are clearly mentioned and they verify your caste as per that register.

Moreover while filling forms like that of CAT, you might have been asked to specify your caste and a link of the same was given next to the box. Had you clicked on the link you would have been directed to the whole list and the mentioned the number against your caste. 

Anyway, ultimately you will have to present only the most recent,  central government issued NC-OBC certificate as per the amended database. 

All the best!!