When a bankruptcy case is first filed, notices are mailed out to all of the listed creditors. The notices contain information about deadines for filing “proofs of claim”, and lists objection deadlines for issues a creditor may have with a case, or for the filing of an adversary proceeding (these are not common).
It is the creditor’s responsibility to see that its proof of claim is filed on time and in the right format with the bankruptcy court. Its failure to do so can mean that it will not share in any assets of the bankruptcy estate. If a claim is not timely filed, a creditor would have to show the court that its failure to file on time was due to some “excusable neglect.” This is not easy to show.