When Elvis and Marie go to escape the crowd, Marie asks Elvis, "Can you row a boat?" Elvis replies "Can I row? Didn't you ever see 'King Creole?'" - Elvis did have a scene on a boat in "King Creole," but it was a steamboat... no rowing required.
The beginning of the film says it is a fable about Elvis Presley. A fable is sometimes, but not necessarily, a story that features animals or inanimate objects that behave like humans.
The jet in the movie ending is a Cessna Citation 500. Although commercially available since 1971, the airplane on the movie (registry N888GA - cn 500-0132) was built in 1973, one year after the movie events.
The setting of this movie was 1972. It features the song "Drift Away" by (the late) Dobie Gray, which wasn't released until 1973.
This movie was set in 1972. Johnny holds a copy of the single for "If I Can Dream" on a black label with RCA's Nipper. RCA didn't use that sort of label until 1977. Between 1968-72, RCA used an orange label without the Nipper.