You are right that no court has yet ruled that a specific set of human contributions to AI-assisted work was sufficient to establish authorship. What exists is the inverse: the Copyright Office has granted partial registrations where human-authored elements were separated from AI-generated elements, as in Zarya of the Dawn, where the human-written text was protected but the Midjourney images were not. The Allen v. Perlmutter case pending in Colorado is the first direct judicial test of whether iterative prompting and editing can constitute authorship. Until that decision, the positive threshold is genuinely unknown. The piece reflects this in the calibration section at the end, though your point is worth adding to the authorship discussion more explicitly.