SMW stupidly default that if you're using a sort key, that key must exist in all objects. If filters out all objects that don't have the key, then sorts by key -- when you want the opposite. But there's an experimental feature to get around it.
- https://www.semantic-mediawiki.org/wiki/Help:Sorting
- (First Blue Note field describes it).
- Sorting Features: https://www.semantic-mediawiki.org/wiki/Help:$smwgQSortFeatures
