Board Thread:Inclusion debates/@comment-31010985-20170427135811/@comment-24894325-20170427155055

Wait, but wasn't it discussed very recently that we don't really care how many additional universes are involved and which characters from them are there. These are stories involving the Doctor, right? So DWU. They are licensed; they are stories; they are released. A story involving any of the Doctors cannot, IMHO, be intended to be set outside DWU in any reasonable sense of DWU, however restrictive.

Put it another way, the fact that Walter the Worm belongs to some other universe is, strictly speaking, out-of-DWU information. All we know is that it met some of the Doctors. I would say this is no different from the Doctor meeting Robin Hood, who is also a literary character, or meeting Gulliver in the Land of Fiction.

And of course, there were plenty of crossovers on a much larger scale, such as Assimilation² involving a big chunk of Star Trek universe.