Never use IMDB as a source for TV series, it's very rarely correct.

Always use the website of the original broadcaster.

In this case, that is BBC. As per their website, there are only 7 seasons of the show and a lot of standalone Special episodes.

https://www.bbc.co.uk/programmes/b006xthd/episodes/guide

The data here on TMDB for this series is correct.

Hmm... "correct" or not, there is a season 8 and a season 9. From my point of view, imdb is correct, it shows all the seasons/episodes that exist. I have them, I've watched them many times :) Tmdb is missing 2 seasons, how can I add them to my library then?

Tmdb should focus on the actual show/movie title, not the production house/broadcaster/etc.. I don't care who made the last 2 seasons, fact is they exist and are a part of that show so should be available in the library.

There is not a Season 8 or Season 9. There never has been.

The episodes that IMDb lists as Seasons 8 and 9 are Special standalone episodes not part of any season, as per the BBC website. The episodes are therefore correctly listed in the Specials season on TMDB.

https://www.themoviedb.org/tv/72-only-fools-and-horses/season/0

As gillybeavis explained the BBC did not broadcast the episodes as season 8 and 9, so the list is correct. There’s nothing that needs changing.