When did 6 become 5?

[tnb]

Looking at *most* of the contemporary reports (ie the 'picture papers') of the discovery of MJKs body, they almost all seem to count her as the 'sixth victim of the whitechapel fiend' (or something similar)

So - simple question; when, and perhaps more interestingly WHY did (I'm guessing) Tabram go from being canonical to non?