The Gang Makes Lethal Weapon 7 - S15-E2
Trivia: The opening premise is the local library removed Lethal Weapon 5 and 6 because of insensitivity and use of black face. This is a reference to Hulu pulling 5 episodes of "It's Always Sunny in Philadelphia" in real life because the episodes contained black face, including the Lethal Weapon 5 and 6 episodes.
Answer: It's been a while since I've seen the film, so take this with a grain of salt. This is hard to explain, but the way I always took it was that when Seth failed to kill his future self, it began to continually alter time/the timeline. Thus, time has to sort-of "catch up" to the older Seth. Which would explain why his wounds appear in "real time" based on what's happening in the present... time is "catching up" to him as the timeline is further altered. If I recall correctly, something similar begins to happen with OId Joe where he begins to remember Young Joe's actions as he performs them.
TedStixon