The onscreen titles of the first 12 "Treehouse of Horror" episodes of The Simpsons were given as "The Simpsons Halloween Special". "Treehouse of Horror XIII" was the first to be called "Treehouse of Horror" onscreen.
However, according to a number of online sources (1, 2, 3), the first 12 specials are all titled "Treehouse of Horror", despite the different onscreen title. Were these episodes always titled "Treehouse of Horror", despite the onscreen title being "The Simpsons Halloween Special" or were the titles retroactively changed?