This was Chadwick Boseman's final film to be released in his lifetime. He has one other Netflix film to be released later in 2020: Ma Rainey's Black Bottom (2020). Chadwick worked on both films while undergoing treatment for the colon cancer that ended his life.
The five "Bloods" seen throughout the movie in present-day scenes are named Paul, Melvin, Otis, Eddie, and David. These are also the individual names of the five members of African American vocal group The Temptations. Their fallen "Blood", who was the leader and inspiration for the others during their days in the Vietnam War, was named Norman. Songwriter Norman Whitfield produced virtually all of The Temptations' music during their time at Motown Records during the '60s and '70s.
The film was originally titled "The Last Tour," and it was written by Danny Bilson and Paul De Meo to tell the story of four aging white vets who were heading back to Vietnam. Oliver Stone was attached to direct at one point but moved on. Producer Lloyd Levin read in an interview that Lee's favorite film is The Treasure of the Sierra Madre (1948), and thought Lee would appreciate the similar elements in "The Last Tour." Lee liked the premise, and he and his co-writer, Kevin Willmott, rewrote the script to make it about Black soldiers.
According to an interview with Giancarlo Esposito he was in talks to be cast alongside Samuel L. Jackson, Denzel Washington, and John David Washington; however due to scheduling conflicts, it fell apart.
The reason the characters appear old during the war flashbacks is that it isn't a flashback; it is the characters remembering the past, so they remember the past with their current age. It also symbolizes that in their minds, they are still in Vietnam and will continue to be in Vietnam, never fully being able to move on from that war.