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Okay, I'm claiming this as foreshadowing before someone else does so I can feel smart! XD (Wag the Song - Season 10, Episode 14)
Tammy - My song name-checks every kid in school in locker order, 'cause who's not gonna clap for their own dumb name? ( scoffs ) ♪ Willa Prentiss, Hogarth Haber ♪ ♪ Lily someone, she's my neighbor. ♪ It's extremely unluckily it's Lily Belcher because I doubt they would leave a locker vacant that long in a public school. (What do I know though, I was homeschooled XD). The fact that they didn't give Lily a surname implies something at the very least.
What it implies is the joke was supposed to be how it's sad Tammy doesn't know the last name of her locker neighbor. The fact she knows her first name also implies Lily is a kid that is currently alive and in Wagstaff. So this possible foreshadowing is doa.
I just thought it was interesting. I google searched transcripts of Bob's Burgers episodes and found the word "lily" was mentioned 3 separate episodes before the reveal of Lily Belcher but only twice referring to a type of name. The last one isn't worth bringing up because the scene was only referring to a shade of white.