Generally, you either know something or you don't. There's not a huge amount of difficulty in that. The difficulty is defined by how many people will know them. If you knew them all, congratulations; many others clearly didn't.
I always mix up Seventh Seal and Seven Samurai, so I tried spelling "Kurosawa" seven different ways. Ditto for John Carpenter and Wes Craven; I can never keep them straight. I knew WALL-E was "Andrew...something," and I only got Terminator 3 because I remember Christian Bale kept shouting "McG!" in that video in which he goes completely insane on the cinematographer. Fun quiz.
The Home Alone director is just Chris Columbus, not Christopher. I checked the film credits on IMDB, as well as his Wikipedia page, and I can find no reference that he has ever been called Christopher.
True! From The Guardian (2013), "His father, Alex, the son of Italian immigrants, named him “Chris not Christopher, because of a long-lost wish by his father to have a Chris in the family.” (Columbus’s grandmother had refused to inflict the name on any of her 12 children.) “Most people think I’ve changed it to Chris and I say to them, ‘Are you insane?"
Anyway, easy peasy.