Shatner and the Reeve-Stevens are free to create their own origins of Kirk and Spock meeting up, of course, since they are not contradicting any existing canonical Star Trek adventures, or even previous ST novels, except maybe a trilogy of "young adult" novels. This situation is no different to DC Fontana's "Vulcan's Glory", which specifically (and purposely) made the claim that Spock was the only son of Sarek in the lead-up to the release of "ST V: The Final Frontier", which was to feature Sybok.
The so-called "Shatnerverse", as written by Shatner and the Reeve-Stevens, already exists in its own continuity. Now nine books become ten. No problem.
If there's time, the ST authors can be requested to tweak their proposals and manuscripts to match changes brought about by impending/current canonical events. For example, Jeri Taylor had to revise "Pathways" to add Seven of Nine to the framing sequence, and to have Neelix channel the missing Kes's backstory. The Remans (of "Nemesis") had to be incorporated into the latter parts of the "Vulcan's Soul" trilogy by Josepha Sherman & Susan Shwartz.
But both of those rewrites caused scheduling delays, IIRC. So we end up with cranky fans no matter whether future canon is anticipated or not.
Awaiting the next collision course...