Helga Blabs It All / Harold the Butcher - S3-E1
Corrected entry: The dental hygenist's hair changes color from red to brown.
Arnold Betrays Iggy / Helga and the Nanny - S3-E10
Corrected entry: In Helga's dream, her slippers start out pink, but when Inge goes after the pigeon, they're white.
Correction: It's her dream, not real. Helga can change whatever she wants in two seconds in her dreams.
The Aptitude Test / Oskar Gets a Job - S3-E9
Corrected entry: When Eugene dropped the tests, just about all of them fell out of their folders, but apparently only Harold and Helga's were switched.
Correction: We don't know that definitively. Those were just the only two caught as the teacher noticed their tests were very off from who they were as students. He didn't appear to check any of the others for mix ups.
Crabby Author / Rich Kid - S3-E17
Corrected entry: In "Rich Kid" Lorenzo is introduced as a new student, but he was in a previous episode titled "Arnold's Room."
Correction: Other than the few episodes where a specific time of year is taking place; these episodes are not meant to be taken to be shown in chronological order. Just roughly in the same 4th grade school year.
Correction: I agree with the other correction, but it's also worth noting that in the production order, "Rich Kid" was made before "Arnold's Room." They were just aired out of order, just like many of the other episodes.
Girl Trouble / School Dance - S3-E18
Corrected entry: Girl Trouble: Arnold somehow does not see the huge pile of glue that Helga put on his chair before sitting down. (00:03:14)
Correction: Plenty of people don't look before sitting down. I once had someone put a pin on my seat in school and I didn't see it.
I can understand one not catching a small pin on their seat (or clear coloured glue). In fact, that is a pretty common prank. The thing is, Helga put a whole bunch of white glue on Arnold's chair, something so blatantly visible, unlike the other stuff I mentioned. It's just strange to me that Arnold wouldn't see something like that before sitting down in his chair. This also goes for my other entry that you added the same correction for.
Correction: No, it's auburn. Auburn hair has red highlights in it, so sometimes it looks red sometimes it looks brown.