I only scanned the photos (and the front cover) but at a fairly hi res. then reduced it.
The track plan he supplied to Model Railway News (which they may have redrawn as a black on white line drawing for clarity) looks to have been slightly earlier than this better known version
It has one fewer spurs off the turntable and doesn't indicate a future extension from Daphetid though he does mention that in the text. This version is also more detailed so may have been redrawn when John Allen had already scenicced part of it.
The turntable, along with the engine house, was always on his first plan so I assume, and the book seems to confirrm this, that he didn't finally decide to make that area into an industrial zone instead until he'd drawn up the plan for the first extension with the shed and the first spur of the 3ft gauge D.G. & H in front of the original baseboard. That's the version that appeared in Meandering About the GD Line in the Jan and Feb 1950 HO Monthly though some of the photos illustrating that article are of the layout before that extension. There was a later selection of photos, but no further article by John, in the September 1948 Model Railway News, Old G&D Engine no 8 and Her Home that does seem to show the engine house on the front extension though with no sign of the turntable and with photos taken from both sides I suspect it was actually a staged diorama placed in front of the layout for one shot. It's also possible that these photos were sent with those used to illustrate John's March 1948 article and simply held over by MRN's editor. There is no article about the shed
In his March 1948 MRN article John talks about the oriignal 3ft 7ins x 6ft 8ins original layout as being portable. That would have been compromised by the addition of the extra section but he was already working on the room in order to incorporate it into a larger permanent layout. What isn't clear is whether he originally intended to make the original board removable as a portable stand-alone layout. It only had one connection to the engine shed board pus whatever connections there would have been at Daphetid so that would have been entirely feasible. However, he also adopted the very sensible policy of ensuring that as he extended the layout he still always had a working railways to operate.
In any case, looking at the plan of the first large G&D and photos of it in the book that original layout seems to have thoroughly absorbed into the larger network fairly rapidly. though it's still very apparent as a piece in the final layout.