Originally Posted by Face_Palm
1989 to 2008 was 19 years and the film reflected that. Last Crusade was in 1948 and Kingdom was 1967.
2008 to 2020 is 12 years so from Kingdom which was 1957 will be 1969.
That's only happened once though, and was a last minute decision.
As late as City of Gods, Indy 4 was going to be set in the early 50s. I think '57 was chosen because KOTCS was at the time toro ably felt to be the last Indy movie, but also the year it is set in is topical in a way to the events of the film: The Soviets launched the world's first satellite, Sputnik, in 1957, thus starting the space race.
LC was made 8 years after Raiders, but set just two years after. There's no hard set rule that the films in universe dates have to correspond with the passage of time between filming.