In other words, a turn can't be anaphorically and rhetorically dependent on a turn that comes after it.
the nature of dialogue imposes an essential and important constraint on the attachment process that is not present for monologue or single-authored text, where an EDU may be dependent upon any EDU, later in the ordering or not: in dialogue there are no "backwards" rhetorical links such that an EDU in turn n by speaker a is rhetorically and anaphorically dependent upon an EDU in turn n + m of speaker b with a = b.