Board Thread:The Panopticon/@comment-4028641-20150828141837/@comment-1827503-20150916222453

My personal belief is that a multi-Doctor story is one where multiple adult incarnations of the Doctor play a part in the narrative, and the reason for the appearance of multiple incarnations is not the Doctor's regeneration. For the purposes of this rule, "incarnation" is defined as the numbered Doctors plus the War Doctor.

This is worded specifically to exclude Listen and the retro-regeneration stories, while allowing Deep Breath.

In addition, this wording counts the Meta-Crisis Doctor as if he were the Tenth Doctor because the two are the same incarnation, so Journey's End is not multi-Doctor, but a hypothetical meeting between Meta-Crisis and any other incarnation of the Doctor would be multi-Doctor.