Also about the hole on the activation band I have the licensed replica released a few years ago and it is a great piece which I believe is 100% screen accurate to the version used by Tom Baker in his first story (robot) as the body is perfectly matching any screen clips and the emitter is also screen accurate to one of the versions used as you may know there were many emitter heads as these needed to be replaced every so often due to breaking
However the hole on the activator ring you are right we do not tend to see this on screen however I think it would have been present in the prop as I personally think it was there to show where to place the thumb so that the hole in the top of the collar is facing the front towards the camera just so the actor knew which direction to run the collar as it could be turned around to look like the setting was changed
Hope this helps