Please remove episode 9 from season 1. It is actually the start of season 2.

Source please? Where can I see the season on the original network's website?

This is the best source: https://app.nlziet.nl/series/8aWR6vkti0aCVRq20fkITw/Oyjjohb1ckO7PFVuLYxqBQ The network itself doesn't care that much about seasons and episodes: https://kro-ncrv.nl/programmas/onze-boerderij

I expected that rearranging the seasons would be done after the removal of episode 9 of season 1. But it wasn't. And it seems that rearranging also added duplicates.

Season numbering is now according to year. But seasons 1 and 2 have an incorrect number of episodes. Season 1: only 4 episodes. Episode 5 to 9 should be removed. Episode 6 to 8 are duplicates of 1 to 4. Episode 9 is also a duplicate of 1. Season 2: only 6 episodes. Season starts on 08-09-2020 and ended 13-10-2020. Episodes 1 to 4 should be removed. Episode 5 is 1, 6 is 2, 7 is 3, 8 is 4, 9 is 5, and 10 is 6. Season 3: episodes are correct, but episodes 3 to 6 all are a week to earlier. There was no airing on 20-09-2020 (September 20th 2020) Season 4: is correct, same as nlziet

Thanks for all your help.

But seasons 1 and 2 have an incorrect number of episodes.

Removed. It wasn't clear from your first report that half of the episodes you added to the first two seasons were duplicates.

Season 3: episodes are correct, but episodes 3 to 6 all are a week to earlier. There was no airing on 20-09-2020 (September 20th 2020)

Done.

I also had to fix the fake episode names (1, 2, 3) and overviews that were often cut-off in the middle of a sentence...

Thanks for your help, everything looks as it should. Great work!

Next time I will try to describe the problem better.