The blue spot in Lisa's hair constantly changed sides.
Lisa's pearls turn from white to red when she meets the coding teacher and then back to white.
Marge's post that gets Homer fired from the nuclear plant is dated August 5th. However, Lisa is shown to be attending school along with her entire class. Springfield would not have school that early in August, and if they did it would be summer school with smaller classes (either remedial students, or kids like Lisa who wanted to take extra coursework). However, school start dates are based on individual school districts per year, and do move earlier in the year occasionally. Springfield may start as early as the 5th of August. Additionally, Lisa's class is primarily nerdier kids, who may be there for summer school. Bart, on the other hand, may have been forced into a remedial program over the summer.