Out of date, but.......
CAP 737 is still regarded as the CRM standard, even though it is out of date. '737 is in the re-write process. This document is still the best that there is with regards to CRM.
Treat CAP 737 as a 'dated' document with improvements to come but the core information is still all relevant. Course providers still use it as their base as there is still nothing available.
There is a Standards Document 29, which does take its place but does not go into any detail like CAP 737.