If you look up 'International Phonetic Alphabet' or 'Vowel', you will find the above diagram, labelled as 'IPA Vowel Chart'. This clearly has additional symbols that don't appear on the IPA Chart. It also appears in the article on 'Vowel Diagram', but there I decided to amend the captioning to make it clear that the diagram was not standard IPA. So far, no objections from other editors. The chart in the article on 'Cardinal Vowels' has the classic diagram.
As a separate matter to discuss some time, the 'Cardinal Vowel' article contains, near the end of the article, buttons on each symbol with recorded audio. A lot of the vowels sound to me rather far from the expected quality - any views on this?