Board Thread:The Panopticon/@comment-4028641-20151101035254/@comment-9435571-20151119020822

But for disambiguation we use the story in which a character first appeared in terms of release chronology, not internal chronology (so the original Osgood being in "UNIT: Extinction" doesn't matter). Both the original Osgood and her first Zygon double first appeared in "The Day of the Doctor".

By the way, "UNIT: Extinction" is the name of the anthology, if anything it should be "Osgood (Vanguard)", the first individual story in the set.