[High Praise! to Den of Geek]
Time Trap: How Escape From the Planet of The Apes Was Ahead of Its Time
Feel free to nitpick my title and name other prequel-sequels that were made prior to 1971
[Think you have a link that’s IMAO-worthy? Send it to harvolson@gmail.com. If I use your link, you will receive High Praise! (assuming you remember to put your name in the email)]
Ben Hur was the prequel to the Greatest Story Ever Told.
Charlton Heston was in a lot of prequels.