Each of the three persons can shift to either of the other two, making six directional possibilities. The count concerns discourse perspectives, not the sheer number of verb or pronoun forms.
Initial perspectivePossible later perspective
First personSecond or third
Second personFirst or third
Third personFirst or second
For example, an entity previously referred to as absent may become the immediate addressee. If two grammatical persons simply refer to wholly different participants without a contextual turn in the same discourse, the example cannot be classified merely by counting the pronouns.