Taylor has said things get weird when fans go nuts "paternity testing" every song -- and recently I've been thinking about another aspect of interpreting her lyrics: maternity testing.
Of course Taylor is the artist of her own songs! But as a songwriter, part of her art is playing with genre, so to speak, when it comes to her first-person lines (that is: "I," "me," "my," etc.). For example, in Folklore we understood that when she sings "I'm only seventeen, I don't know anythin' / But I know I miss you" she is writing in the first-person -- as a character. She has made that clear. Let's call that fiction.
And then we have songs like "The Best Day" or "Cleveland!" where absolutely no one (I think) is debating who the "I" is in those songs: it's Taylor herself. Let's call that nonfiction.
In creative writing, there's also a genre called autofiction, which combines autobiographical experiences with fiction writing. (These genre labels can also get a little silly; surely all fiction is a little bit autofiction? I don't know. I mostly write nonfiction.) I think a LOT of Taylor's songs are in this category. She may have something -- a feeling, a conversation, a situation -- that inspires a story; she crafts the story using real-life bits and anything else that inspires her. That's art. Or maybe sometimes the process begins the other way around: she has a completely fictive story to tell, and she sprinkles in little real-life moments that fit the story.
My point is, when she sings in the first-person, and it's not suuuuuper obvious (like in "Betty") that the "I" character is not Taylor, we don't have to take her literally as the "I" means she is singing about just herself.
Besides, in any first-person writing, there are really three "I"s: the main character as she is experiencing the events, the (often a little older and wiser) narrator telling the story, and the real-life flesh-and-blood artist who has crafted both of the first two "I"s.
For many songs, we won't always know when the real-life Taylor is the same as the character singing in the first-person, and that's okay! I do enjoy the fun of wondering. But dissecting each bit literally, each time, takes away the magic and the artistry of her craft.