The three words on your coffee cup are usually blamed on a 1994 lawsuit. The documented record shows a severely burned woman, a jury that assigned McDonald's 80% of the fault, and a settlement whose figure was sealed and has stayed sealed, but no dated proof that the warning itself began there.
No federal rule requires a 'refrigerate after opening' label on ordinary condiments. The phrase's closest documented ancestor is a 1997 FDA guidance that FDA itself called nonbinding, and that gap is exactly why the words are everywhere.
California's most recognizable warning sentence isn't in the statute at all. It's regulatory safe-harbor text layered on top of a 1986 ballot initiative, revised once in 2018 for specificity, and pierced once, for coffee, by litigation.