When source material exists, how do 'Screen Story by', 'Screenplay by', 'Adaptation by' and 'Based on' credits work in the WGA manual?

In the WGA manual, 'Screen Story by' goes, only through arbitration, to a writer who takes just a springboard, character or incident from story-type source material and builds a substantially new story; the source author then gets a form-of-acquisition credit. 'Screenplay by' fits when story-type source material exists. 'Adaptation by' is generally opposed and only awarded by arbitration in unusual cases. 'Based on Characters Created by' goes to writers holding separated rights on sequels. Curator qualifications: Manual read 2026-10-22 (curator text extraction of the pinned PDF); no credit determined. Guild credit-arbitration procedure for WGA-covered work, not copyright or legal advice. Section I.5 credit list on the web page (S1) carried from producer reading; PDF read instead. Limitations: Manual read 2026-10-22 (curator text extraction of the pinned PDF); no credit determined. Evidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.

{
  "citations": [
    {
      "url": "https://www.wga.org/contracts/credits/manuals/screen-credits-manual",
      "note": "Screen Credits Manual PDF, Section III credits 3 (Screen Story by), Screenplay guidelines, 5 (Adaptation by), 8 (Based on Characters Created by)"
    },
    {
      "url": "https://www.wga.org/uploadedfiles/credits/manuals/screenscredits_manual21.pdf",
      "note": "Screen Credits Manual PDF, Section III credits 3 (Screen Story by), Screenplay guidelines, 5 (Adaptation by), 8 (Based on Characters Created by)"
    }
  ]
}