The flashback notes it was 10 years prior to the episode. However, young Kara was age 15 at the time, and adult Kara was age 25 in the Pilot. This should note the flashback was 12 years ago.
Young Kara asserts that she is 'literally bulletproof,' while in the pilot episode, adult Kara is unsure if she is.
J'onn J'onzz appears in this episode in the form of Kara's Kryptonian mother. However, there was no way for him to know what her mother looked like considering it had previously been stated that he can't read Kryptonian minds.
When Kara first gets into bed after her argument with Alex the handle of the coffee mug on her nightstand is pointed to the right towards her. When she goes to turn off the light the handle is now pointed to the left away from her.
Young Kara and Young Alex are in the same grade in high school, yet when they are grown Alex is several years in her career ahead of Kara.
Teenage Kara's ears are visibly pierced, even though her skin is supposed to be impenetrable.
In shots of the school's hallways, the locks on the lockers are all unlocked and positioned identically.
The plural of "nemesis" is "nemeses," not "nemesi."