Hey,

Sorry to say it's not valid  and you need to get your reservation certificate updated. The CAT at the time of registration ask about the reservation of the students and thy are even required to submit their category certificate  at the time of form submission.

If it's expired I will suggest you to get it updated from your nearest block office  as soon as possible in order to avoid any kind of problem in the end or at the time of form filling.

Hope that helps.

Thank you.