"I changed the perspectives because in 'That's When', we originally wrote it as if it was- like, it wasn't a duet originally, it was originally about like a girl who, you know, the person she loves comes to her and says, you know, 'I need some space from the relationship', and she's like, 'fine. whenever you want to come back, you can'. And I kind of just, over time, sort of wanted to change the story into- it's me singing about me needing space from a relationship even though I love that person and that person being gracious enough to be like, 'take your time, whatever you need'. 'Cause I just hadn't really explored that angle before, of like needing your independence and somebody granting it to you, and that making you want to come back to them because you realize that they're the type of person who's always gonna let you explore and grow and that that means that they're the person for you. So, yes, it did change a little bit, but absolutely minimal things. You're mostly hearing from a seventeen or eighteen-year-old brain."
April 16, 2021: Taylor explains that aside from a perspective shift in her song 'That's When', the Fearless Vault tracks have had only minimal changes. (source)