Since a hymnal has a date field, why does each hymn instance have a "publication date" field? This seems both redundant and inefficient.
On second thought, I can see where it could be useful for "hymnals" that don't have a specific publication date, such as the virtual hymnals CCEH, The Cyber Hymnal, Timeless Truths, etc. But in all cases where a hymnal date has been provided, I would think the hymn instance date would be unnecessary.
You may leave the publication date fields blank for the text and tune instances.