Catherine Keener (Maya Sorian) plays both her younger and older selves through the use of shoddy deepfake technology as opposed to CGI de-aging, which typically is used in big-budget movies/series.
A bullet wound, whether transfixing or not, through the abdomen, making "fart noises" when coughing reveals an obvious digestive tract perforation which will lead to infection, sepsis and death if not tended to by a qualified surgeon.
In one of the fight scenes, Adam is asked "has anyone ever told you talk too much?" This is the same line project X is asked in X-Men orígenes: Wolverine (2009), featuring Ryan Reynolds. It's also the same line asked in Deadpool (2016), starring Ryan Reynolds.
When sitting outside the motel, the younger Adam says he first saw the backstop in the window at Altman's. This is a reference to Hasta que la Muerte los Juntó (2014), also directed by Shawn Levy and written by Jonathan Tropper, in which the principal character's family, the Altmans, own a sporting goods store.