Thats an interesting point you bring up regarding the dates etc. When talking of TKD, we are talking 1940's to present day. For this specific subject we are talking 1940's to when the word MMA was used in the vein it is now (late 1990's I think). Thats a lot of years to cover.
I think its getting all messed up because "continuing on the ground" is getting sided with being the same as MMA (as it is today). Until they are accepted as different, they continue to add to the 'is it/is it' not type of argument. I say again, the focus of moderm MMA is much more advanced on the ground than any "follow ups" that were taught in TKD. As you (ITFunity) have said, if a fighter goes down and continues to resist, it stands to reason a ground fight will ensue.. the tactics, stragety and techniques of MMA were not about back then.. so how can they be the same!
Further to this, theres the instructors preference, would they allow it or would they not.. plus the instructors history and own learning and influences.
I think a certain poster here is looking for someone to say it was common practice, accepted on a wide/mainstream scale like patterns of something.. which, personally, I dont feel it was. I see it like "alternative/better" boon hae.. the main stream simply followed the normal stuff, but there were TKD instructors that wernt happy with some applications and taught their own because they were more effective in their opinion.. again, not a main stream practice, but there.. but that was the structure of TKD back then.
Most already know of Gen Chois thoughts of being on the ground within early TKD in the military, so anything more than takedown, finish.. I would bet wasnt brought in front of him or at least, the instructors wouldnt have pushed the boundries that way, except in their own schools.
Going back to the date thing at the start of this post, influences over such a massive time period must have been part of it all, so saying it wasnt there (even if there was concrete evidence) at the beginning, doesnt mean it didnt become part of it later on, doubly so with all the Judo black belts involved in TKD (remember Judo already had Ne-waza and randori, so it wouldnt be surprising if these were influences - after all the throws of judo found their way to TKD).
One cannot define TKD as how it was when it very first started, it evolvd over numerous decades and for some, it still is.
The simple point is, if some TKD instructors incorportated following on from a prone position as part of their classes, then this was continued by their students etc. it became part of TKD.. when this occured, who can say really, was it main stream, probibly not, was it accepted practice.. yes by some, probibly not by others. All this is backed up by numerous posters on here across the world who have had it as part of their training (ie. not one single source).
Going back to the "wheres the video" argument.. all the videos posted in the era's wanted (50's 60's) are of demonstration (ie. the main stream stuff), but they were filmed on TV like cameras, no one had a camcorder to take to their club... if they were more common back then and filming was allowed in schools, thats most likely where you would find the evidence sought.. sadly, I dont think it exsists, although hopefully someone will find some.