Although the phrase Griswold vs. Griswald sounds like the name of Clark's (Chevy Chase) latest misadventure, it's actually a much simpler conundrum: the spelling of the National Lampoon's Vacation franchise family's name is complicated. Based on John Hughes' short story "Vacation '58" from National Lampoon magazine, the Vacation movie comedy series kicked off in 1983 with National Lampoon's Vacation — a chronicle of the Griswold family's comedic cross-country road trip to a theme park. Two other installments in the series were released in the 1980s: National Lampoon's European Vacation and the much-loved holiday classic National Lampoon's Christmas Vacation.
https://screenrant.com/national-lampoon-vacation-movies-family-griswold-griswald-spelling/