Thanks for all your feedback, things are making more sense now. So it does look like he was in "a" Welsh Regiment, in his own hand on the application for the AFC he states "2nd battalion Welsh" so I have no real reason to doubt this, though from what your are saying it doesn't quite fit the facts available?
Am I right in assuming that the statement "commissioned in 1917" can't be right and that it was more likely he just joined up in 1917 rather than being commissioned?
Do you think there has also been some licence/loss of understanding overtime regarding "three time Army boxing champion of the Rhine", as my understanding is that the Army Of The Rhine was not formed until 1919 but he was demobbed in Jan 1919, or is the army of The Rhine a completely separate thing and he still could have been "champion of the Rhine"
I have previously looked at all possible variations of William Gladney Davies in the Medal Rolls index and all seemed to lead to a dead end. My assumption is that any records of his relating to WW1 were destroyed in the bombing in WW2, which is why the Army Personnel Centre can't find anything either. This is why I am perusing the boxing angle in case some Army "boxing/tournament" records exist on that might give more information on his Army career.
I am afraid you will have to bear with me on my lack of understanding on how the regiments etc. Worked