Probably the most generous thing you could say is that they were clearly talking to him and sharing information up to around the time of the Queen's death (and possibly up to the catastrophic car chase bollocks, which he appeared to have the inside track on). Then they probably stopped speaking to him after that, in order to have some semblance of plausible deniability at the point of publication of the book - which was supposed to have been in August, but was delayed to allow him to include his sage and considered observations on the coronation.
The last year (and it has been only a year since the Netflix doc hit) has been absolutely bonkers, and seen them lose a lot of good will and become a laughing stock thanks to Spare, South Park, loss of their Spotify deal, candles and feathers etc. But since the summer, with WME coming on board and the relative successes of Invictus and some of their other appearances, it did seem that they were moving on from the RF and into their own niche. So the OS book, which might at the time of conception have seemed to be a good supplementary volume to their own content, is now like kryptonite for them, because it's just dredged everything back up again, and in the most petty and vindictive manner, from the most ridiculous of men who everyone knows has been their close ally and collaborator.