Bill Gunston's 'The Cambridge Aerospace Dictionary' has this to say:
Küchemann tip
Low-drag wingtip following outward-curved streamlines, with large-radius curve from leading edge to corner at trailing edge.
From this I'm surmising that it's the shape in top view that defines this as a 'Kuchemann tip'. The larger camber of this tip is something else again, which did enable the aircraft to operate at a higher cruise flight level apparently. I'm still trying to figure out the how and the why though.
I've been looking at photos of G-ARTA post conversion to see if I can identify the wing chord extension and tips, in the larger version of this image below it does appear that the wing chord extension was fitted. I agree that the performance data in the manuals would otherwise have reflected the different specs of the aircraft had the wing not been modified. From staring at the photos I cannot confirm the tips though.
I don't think that the modified wing was tested on G-ARTA. The 1102 and 1103 VC10s for Ghana Airways and BUA both had the modified wing and I think that they did the flight testing of the modifications on these aircraft (G-ASIW probably as I have photos of this aircraft with 1101 style wing fences and without the downturned tips). G-ARTA wasn't modified for airline service until 1966/67 and by then the BUA and GA aircraft had been in operation for a while. Also they had G-ASGA, the first Super, which was also flying with the newer wing by 1964. With all that I thnk that there was no need to refit the wing to G-ARTA until she was bought by Freddie Laker.
Another question: is anyone able to confirm that G-ASGD was named 'Canopus' on a plaque inside the aircraft as the 'Flagship' of the fleet?