Many aren't very detailed. I could do with more detail on e.g. King's Cross, a station where it's easy to be suckered into a much longer walk to / from your platform if you don't know some of the shortcuts.
The axonometric diagrams are only intended to be used as a location guide. They are part of larger Station Layout documents which have very detailed 2D plans for every part of the station. The axonometric diagrams therefore provide the overall view, including (in the original document) reference numbers for the individual drawings, like a sort of contents page.
King's Cross St. Pancras, for example, has 20+ pages of detailed 2D plans, covering the entrances, ticket halls, platforms, escalator areas, vent shafts and so on.
