Board Thread:The Panopticon/@comment-121.45.54.78-20130925110520/@comment-88790-20130926143649

I think in Mawdryn there's a flashback with the Master in it (I'm possibly mis-remembering).

As to CzechOut's question of what 'counts' as an appearance. We currently count cameos and flashbacks. So, as it stands for example; the Fourth Doctor is listed as appearing in The Almost People and similarly the Ninth Doctor is listed as appearing in The Kingmaker, The Tomorrow Windows and The Eleventh Hour.