Yes, indeed. That all makes perfect sense. I am not sure if you are able to access google drive files but this is the link that I provided earlier to the full traffic order on the RBK website.
https://drive.google.com/file/d/1VH0h-JkSu_5okGFuF0hcgwco-eFnkXIO/view?usp=drive_linkThe traffic order is a big document but there are only a few bits of relevance - the wording of the restrictions and the maps which show the locations of the changes implemented in this order. The maps on kingston vale are on pages 55 and 56. From where it comes off the A3, the maps show that the 20mph has been added until where it meets Kingston hill when it is unmarked on the map (meaning it hasn't changed and remains 30mph), creating a very random gap on Kingston hill which is 30mph. Then the Traffic Order states that the speed limit becomes 20mph again around Coombe Ridings where there is a 20mph terminal sign which I have disputed as being not well located as it is behind a bus stop which is frequently used. As you have pointed out, this is likely to be a slim line of defence.
The map is found on page 66 of the Traffic Order and the rest of the hill is shown on page 72 of the document.
From the bottom of Kingston Vale until the camera by Eastcott Close/ Warren Road, the signage is an absolute mess. If you travel from the bottom of Kingston Vale, we enter a new 20mph speed limit with no signs to indicate this, neither as terminal signs nor any roundels. If you enter Kingston Vale from a side street (Robin Hood Lane or Derwent Avenue), there are new terminal signs indicating that the speed limit is 30mph, when it should indicate 20mph. When Kingston Vale becomes Kingston Hill, there is no new terminal sign saying that there is now a 30mph limit. At the top of the hill, where there are the cameras, there is the first correct terminal sign albeit, arguably, it is not well positioned.
Can the Traffic Order not be challenged on the grounds that the implementation of the new order is deficient? The traffic authority responsible for both signage and the traffic order itself is RBK.