D8 exists as a domain because a lens applied across the other seven domains would have been invisible in every coverage map. The choice has real costs, stated here.
Explainers
Why the framework is built as it is. Structural reasoning. Every article of this type carries the standard non-normative banner.
4 articles of this type
Taught and assessed are different claims. The gap between them is where a coverage map is most often used to imply something it does not say.
An identifier is a contract with every credential that cited it. Renumbering would silently change what those credentials claim, years after they were awarded.
Every awarding body could publish its own competence framework, and several have. The layer model exists because per-credential frameworks fragment the thing they claim to standardise.