File talk:British Isles Euler diagram 15.svg
According to https://www.reddit.com/r/reddit.com/comments/koyfn/distinction/ , there are parts of Scotland (some islands such as Shetland) that are not on the island called Great Britain.
Probably the diagram needs to take this into account too - GB=island(geographically) versus GB=England+Scotland+Wales (politically, including all small islands that are not politically separated).