I imagine number 17 Interview With The Vampire/Interview With A Vampire is because of connected speech. When you say them they sound almost exactly the same, because you only say the "th" sound once (With and The are connected) and the remaining sound*, the "e" in the and "a" are pronounced in a similar way. Your brain only hears that sound and it makes sense in a sentence so it assumes that's the title.
*called the schwa, fact fans, the most common sound in English