The most valid point on this thread so far.

Re: Pre-Hartnell Doctors
This argument has been debated long & hard in some Dr.Who circles...
Basically, there's a Scene in the 4th Doctor Adventure The Brain Of Morbius, in which the 4th Doctor challenges Morbius a/k/a "Chop Suey" to a Mind Wrestling contest...
Fortunately, Dr.Solon's lab just happens to have a full set of Mind Wrestling equipment, consisting of a frame with 2 sets of electrodes (looking like deely-boppers) with a display screen ready to hand.... The Doctor & "Chop Suey" press their heads against the deely boppers, & battle commences....
During said contest, we apparently see images of Pre-Hartnell Doctors after stock footage of the previous 3 Doctors appear on the equipment display screen, while Morbius says "Back doctor, back through your past....".
Apparently, there are 3 explanations for said footage....
1) Morbius is right & the images are those of pre- Hartnell Doctors....
2) Morbius is wrong, said images are fake, as the 4th Doctor is more powerful mentally than he (Morbius)
thinks, & is generating "false" images to buy time & wear Morbius out....
3) Morbius is wrong, in that the images are that not of The Doctor, but previous incarnations of Morbius....
(The Images shown on said screen were those of the production staff involved in the story...)