https://musicbrainz.org/relationship/fd841726-ba3c-47f7-af8e-6734ab6243ff currently says "When a year is specified (as in "℗ 2015 Naxos Rights US, Inc."), use that year as both the begin and end date."  By doing so, the relationship is automatically marked as "ended".

This is not sufficient to capture the transfer of copyrights.

When a company stops existing [1], or if a company transfers rights to another [2], then a new release will mention the same year, but a different company.  I think MusicBrainz should capture this information if it is clear that one of these 2 cases has occurred.

Examples for [1] and [2] overlap:

1. https://musicbrainz.org/recording/b70b5c9f-e449-4615-9d04-ebcaf24af764 - "Sony Music Records Inc." did not exist until 2001, but the copyright statement is given as 1980.  (The original owner printed on the cover art of the earlier releases is not currently linked in MusicBrainz.)
2. https://musicbrainz.org/recording/5dac630b-c3a3-4d32-9580-8ecdd2a4630c - "Konami Amusement" did not exist until 2016, but the copyright statement is given as 2007.  (The original owner is not currently linked in MusicBrainz.)

A possible solution without a schema change is to change the guidelines to only fill in the begin date, leave the end date blank, and only mark the relationship ended if it is known that the company stopped existing or has transferred the copyrights to a different company.

If not that, then a schema change would be required to either,

1. add a field that indicates that the label no longer holds the copyright
2. add a field that indicates that the label did not originally hold the copyright, but acquired it at a later date
3. add a field that captures the year mentioned in the copyright statement to divorce it from the MusicBrainz concept of relationship begin and end dates.  (However, the real begin and end dates of copyright statements would generally be unknown to the editing public.)