alt Hacker NewsVulkan spec is missing tons of stuff. Implementers check they pass the conformance tests (tho those also miss stuff)
directx also has conformance tests.
The directx specs are arguably better in many ways than the vulkan specs. They go into bit level details how various math is required to work, especially in samplers
I'm sure it misses stuff, but generally a 'spec' is better than a 'doc' for the reason that you need enough info to at least guess how a spec is implemented, whereas a doc can leave everything out and as long as the programmer has headers and some examples they can probably do 90% of what is needed.