I'm helping with a project verifying and updating hymn attributions for a collection. I wondered if anyone here has ever found a written definition for when to use different designations relating to different music or text versions of a hymn, such as "arr." "alt." "adapted" "harm." "based on" etc. that would be listed after the composer or author/lyricists names when there have been revisions since the original. I have a general idea of when each of these would be used and how they differ, but I have not found any authoritative sources and wondered if any exist?