Board Thread:Inclusion debates/@comment-1272640-20161226072823/@comment-1272640-20161229064953

Bwburke94 wrote: Under normal circumstances, a story cannot be part of the DWU unless it includes a character or concept introduced in an earlier DWU work. This is an unofficial guideline, but it helps us weed out non-DWU characters who happened to make crossover appearances.

There are limited cases where a story can retroactively become part of the DWU on a character's later appearance, but those are few and far between. Other than An Unearthly Child and the Iris Wildthyme stuff, I can't think of one off the top of my head. What's retroactive about Unearthly Child?