The following information is regarding TuneCore's Publishing Administration service
No, TuneCore does not register songs with the Copyright Office.
According to copyright law, the composer owns the copyright to a composition as soon as it is fixed in a tangible medium (written down or recorded)
Pursuant to the US copyright act, once a work is in a fixed form i.e. recorded to mp3 or CD, or written down, you are protected under copyright laws. However, registering your copyright with the Library of Congress makes this ownership part of the public record. This formal record affords the composer/author additional benefits. In other words, if a work is registered with the copyright office the author/composer has a stronger claim against infringements and better damage compensation as a result of infringement.
You may complete the registration process online at https://www.copyright.gov/registration/
The PA form (Work of the Performing Arts) is the form used to register a composition (lyrics and music)
The SR form (Sound Recording) is the form used to register the master or audio/sound recording only