In episode 377 (3.106), Nora is packing her books for school. She is believed to attend MP1, but she packs a maths book for grade 9.
In episode 466 (5.16), Karin and Erling spend their weekend in Söderköping, but the ship that passes the window is much larger than is usual for Slätbaken - it looks like the ships that sail between Stockholm and Finland