I am quite bad at history but quickly looking at central Europe this project seems to have some inaccuracies.
- I couldn't find any mention of Prussia [0]
- during years 1920-1938 the borders between Czechoslovakia and Poland are messing so it looks like it is a single country
I am sure anyone can find what is missing/wrong with the history of their country. This is a community project after all so I am not surprised but based on Wayback machine this project started at least 7 years ago.