Currently, the main MusicBrainz project includes a short blurb explaining why it has its own version of the revision note for any changes/creations, i.e.

Entering an edit note that describes where you got your information is highly recommended. Not only does it make it clear where you got your information, but it can also encourage other users to vote on your edit — thus making your edit get applied faster.

Even just providing a URL or two is helpful!

BookBrainz should include a similar short description to better explain the purpose of its own equivalent notes to encourage their use.