For a one-paragraph historical narrative of the dominant ninth chord in European and European-influenced music, see this post: link.
[Update 27 August 2026: see the posts for 17 July 2026 and 28 June 2026, which give information and links for a comprehensive index and search methods, respectively.]
On 18 December 2024, I published the fourth and last part in my most recent series: Dominant Ninth Harmonies in Music from 1900 to 1925, Part 4. Here is the link.