I don't think that going into implementation details is what I would expect from an interface specification. The interface exists precisely to isolate the API consumer from the implementation details.

And while they're much better than nothing, those documents are certainly not a specification. They're are individual documents each covering a part of the API, with very spotty coverage (mostly focusing on new features) and unclear relationship to one another.

For example, the precise semantics of ResourceBarrier() are nowhere to be found. You can infer something from the extended barrier documentation, something is written in the function MSDN page (with vague references to concepts like "promoting" and "decaying"), something else is written in other random MSDN pages (which you only discover by browsing around, there are no specific links) but at the end of the day you're left to guess the actual assumptions you can make.

*EDIT* I don't mean to say that Vulkan or SPIR-V specification is perfect either. One still has a lot of doubts while reading them. But at least there is an attempt of writing a document that specifies the entire contract that exists between the API implementer and the API consumer. Missing points are in general considered bugs and sometimes fixed.