@uberwaltz, I can answer your question. But first, let me clarify the issue of the Decca and London names. John Wright had long been a Decca employee (head of the department that made their cartridges), and when he bought the rights to the cartridge name and design from Decca, he changed the name to London. The name "Decca London" can be accurately used only in reference to one of the cartridges made by Decca, the model named the London. Other than that one model, a cartridge is either a Decca, or a London. I see the two names conflated regularly.
The Decca Blue was introduced in the early-70’s, and was also referred to as the Decca Mk.V. It was a drastic redesign of the Mk.IV, and ushered in the new era of Deccas. It had a conical stylus, and tracked at 3-3.5g. It was my first Decca, bought new in ’72 (rhyme unintended ;-). I know, I know, the London website states the Blue was introduced in ’74. But I bought one in ’72 after: 1- reading a review of cartridge by JGH in Stereophile, and seeing and hearing one in the system Bill Johnson delivered and set up at Audio Arts in Livermore, CA that same year.
John Wright will rebuild, restore, update, etc. any and all Decca or London cartridges, including the Blue. Where did you read about a John Wright-rebuilt Blue? The Blue had been discontinued by the time John bought the company, so there is no such thing as London Blue, only a Decca. At least that is my understanding.