Why would me sending a debt collector a CAFV work?

If they are only required by law to give answers according to FDCPA and validation of debt is kind of a gray area as to what it means. I've seen where the law looks like its saying they are only required to give address and name of original creditor, but anybody can get that it doesn't prove anything. Whats to stop a judge from saying they don't have to answer your CAFV by FDCPA law! What makes the CAFV a document that will stand in court if the prosecutor (debt collector) is not required by law to answer it?