I have been following, or trying to follow, this thread and have some observations and a question:
Question first: Do peg notices stating 'unsupported kneeler' exist ? I am not sure I have ever seen one .. although that could be explained by bad memory. I have seen lots of 'compulsory kneeler' and 'kneel or stand' but cannot recall 'unsupported kneeler' or 'supported kneeler'. Of course this does not mean that such positions do not exist, which leads to the observation part of the post.
A 12" peg could well dictate an 'unsupported kneeler' as Sultano indicates, but the fact that you need to touch the peg with foot or leg could define the shot as 'supported' if a leg is rested against the peg. This definition of 'supported' is clearly wrong and in UKAHFT terms the shot would be 'unsupported': there could be no support being given directly to the hand or rifle unless you were considerably vertically challenged, (i.e. neither the hand nor the rifle would be in direct contact with the peg). In practice, therefore, a 12" peg that just states 'compulsory kneeler' need not state 'unsupported kneeler' as it becomes 'unsupported' in UKAHFT terms simply because of the peg size. A flat peg plate would make this position quite clear.
If the peg is considerably taller than 12" or if there is a tree or other support available then a 'compulsory kneeler' could well become a 'supported kneeler' and allow the supporting hand/arm to grasp the support, maybe even allowing the rifle to rest or be held against the support. Of course, the position of the said support may mean that a shot from such a supported position is impossible and the shooter would need to move a little 'off the peg' which still making contact with the peg; such a shot then becoming what you could term a 'forced unsupported shot'.
In all cases, of course, the rules regarding knee, foot, arm etc positions which define a kneeling shot must be adhered to.
In summary, I am not sure what the debate has really been about.
So: are some pegs actually labelled 'unsupported kneeler' in situations where true direct support of the hand or rifle is possible? If so, then I suggest course setters beware and maybe avoid any possible criticism by not using such pegs.