I didn’t realize that either until last week (see post 17). I though “Rusty” looked a lot like a young Leonard Hofstadter so I had to look it up on IMD to be sure. But if I am not mistaken, every “Vacation” movie had different actors in the roles of the Griswald kids, Audrey and Rusty. Johnny Galecki while not particularly a stand out in the role of Rusty in Christmas Vacation has probably had the most commercial success post “Vacation”. The only actors to reprise their roles outside of Chevy Chase and Beverly DeAngelo are Randy Quaid and Miriam Flynn as Cousin Eddie and Catherine.
Anthony Michael Hall, the original Rusty, had a pretty successful career throughout the 80s-90s. Juliette Lewis, Audrey Griswold in "Christmas Vacation" would earn an Oscar nomination two years later for "Cape Fear" and enjoy a great deal of success throughout the 1990s.
Another Griswold who went on to greater fame was Cousin Eddie's daughter, Cousin Vicki from the first movie, played by Jane Krakowski, who would go on to receive multiple Emmy nominations for her role on 30 Rock.