Well, last.fm has been around for 20 years, but at the outset they took no consideration that two "artists" might have the same name. And they still haven't come up with a better solution than relying on users to edit in things like "There are at least 4 artists with the name David Williams".

So, forgive me for thinking their recommendation algorithm may not be exactly state of the art either. There's no inherent reason a recommendation algorithm shouldn't be able to figure out that an omission is intentional.