I would argue "creative license". Not everything must be true. Frank Davis said everything in his book "Sex Rebel" was based on his experience, but the story over all was not true. (He did use the name "Ann" though.) Frank was unquestionably a good writer. I bought his book "Livin' the blues" and it is quite well written and likewise an interesting story. I do think the references in his poem about Madeline are possibly linked to Madelyn Dunham, but I would regard the references to Matisse, penthouses, Broadway plays and Europe are more to be regarded as fanciful compliments meant to represent her dreams and desires. Possibly an effort to curry favor from her as a form of flattery. A Statement regarding her tastes perhaps.
Do you find it odd the Frank Marshall Davis’s post-humous biography ‘Livin the Blues’ went silent during his years in Hawaii?