The most iconic "subtitle" in the film isn't dialogue at all, but the Day Counter transitions.
I. Introduction
When Marc Webb’s indie darling (500) Days of Summer hit theaters in 2009, it rewrote the rules of the romantic comedy. It wasn’t a love story; it was a story about love. Starring Joseph Gordon-Levitt as the hopelessly romantic Tom Hansen and Zooey Deschanel as the commitment-phobic Summer Finn, the film’s non-linear narrative captures the dizzying highs of expectation and the crushing lows of reality. 500 days of summer subtitles top
Studies in Flashbacks: “(500) Days of Summer” | by Scott Myers Summer's response to Tom's declaration of love highlights
He tabbed over to a film forum where he had been arguing with a user named CineastTom . “You’re wrong,” Leo had typed earlier. “The subtitles aren’t just utilitarian. They are the emotional compass. When we jump from Day 288 to Day 1, the subtitle at the top is the only thing keeping us from getting vertigo.” but the Day Counter transitions.