If you're suing someone for making MP3s available on a P2P network (uploading), it doesn't matter whether you can look in the ID3 tags of those files and find comments that show they were ripped by a dedicated group. It doesn't matter whether you can compare MD5 hashes of those files with those seen on any particular P2P network. It doesn't even matter whether the person owned the CDs or not.
The only thing that matters is whether putting those files there, even if no-one downloaded them, was illegal (and, of course, whether your online anonymity should be destroyed in response to one unaccountable request).

Nycfashiongirl attorney Glenn Peterson dismissed those claims as irrelevant to his client's current motion. The Kazaa user is contending that her rights are being violated by the subpoena for her identity through Verizon and is not yet fighting a lawsuit accusing her of infringement, he said. [ZDNet]

Court motion (PDF, from EFF)