The expired caste certificate hold actually no significance and it might be your categiry certificate is regected in the later stage of online admission itself. If that happens, then you have to fill the form again and submitting your revised/latest category certificate.

Also I would like to mention, if this form is accepted during the online submission then it would be straightly cut or rejected during the physical registeration. So I would recommend you to issue your latest caste certificate to reap the benifits of being an SC