Thanks for the heads-up! The count_dataset method is pretty new, so it seems like I forgot to add this when it was introduced. Just updated the docs and should be live in a few minutes.
Database.db is technically an attribute and uses whatever is passed in as db on initialization. So I think that's why it's currently only documented on Database.__init__. We could add an "attributes" section (similar to how we do it in the spaCy API docs), but there are currently only 3: db, db_id and db_name.