Is there a difference between Black Lager and Dark Lager, or is it just the name?
Since the recipes for Dark/Black Lagers seem to be quite varied, it is hard to tell if there are any majorly different components.
It's likely just naming differences. Though the BJCP has distinct categories for "Dark American Lager" and "Schwarzbier (Black Beer)". The main difference seems to be that Dark lager is sweeter and more towards caramel malt than Black which is more dry and slightly roasty.