Board Thread:The Panopticon/@comment-197.86.143.126-20200606192351/@comment-6032121-20200710151537

No, that post is not enough. Even if the Deca flashbacks themselves in Divided Loyalties are clearly unreliable, the Epilogue, which is not from an unreliable point of view, clearly describes Koschei and Magnus as two different individuals, stating that Koschei went on to "try to become the Doctor's Master" while Magnus tracked down "the Aliens and their War Games" and eventually got killed.

But as has been said several times before in this thread, this does not matter. It can be the case that some valid sources say X and Y are the same, and another does not. Just look at Goth and Pandad IV.