Board Thread:The Panopticon/@comment-27321963-20200710123549/@comment-27321963-20200710222525

I am not saying that they are exactly the same incarnation (like your example of the First Doctor). But we are quite clearly told that they are incarnations of the same individual, and this is compared to the Doctor's many lives (not just me pulling that comparison out of thin air).

The difference is that Bernice Summerfield identified Daughter of Mine as Aphasia, you could not have a character visually identifying those versions of the Master without knowing more about them.