These guides provide walkthroughs for specific kernel development tasks. For example, there is a guide on how to add a new syscall interface for userspace applications. The guides are intended to be general and provide high-level instructions which will have to be adapted for the specific functionality to be added.
Overtime, these guides will inevitably become out-of-date in that the specific code examples will fail to compile. However, the general design aspects and considerations should still be relevant even if the specific code details have changed. You are encourage to use these guides as just that, a general guide, and to copy from up-to-date examples contained in the Tock repository.