Corrected entry: Earlier in the series Slater said more than once that he was an only child. All the sudden he has a sister.
Corrected entry: Lisa, Zack & Screech all talk to JB as if they have known her since she was little. However, they have only known Slater for approximately four years, so them knowing her from a little girl, as implied, wouldn't be possible.
Correction: JB is only featured in one episode. The fact the kids knew her already (even if up to four years) doesn't mean she was known since a little girl...just that they all previously met her at some point.
The New Girl - S4-E4
Corrected entry: When Zach gives the presentation for the electronic date book, the lockers seen out in the hallway are all light blue. When Tori and Zach walk out that same classroom, into the hall, all the lockers are now orange.
Correction: The lockers seen from the view inside of the classroom are from the other hallway by the bathrooms. They are in fact blue. However we never see the main hallway lockers that are in fact orange in that camera's view.
Correction: Slater never said he was an only child in any episode. Only Zack and Screech have each confirmed they were an only child (Screech confirmed it in this episode). JB was just never mentioned before this episode. His mother was never seen in the whole series, but she still could have easily existed.