The thing that checks it is not the thing that wrote it
The cases the work relies on are looked up in the published case law. A case that cannot be found is flagged, not assumed. Then a separate checking stage, which wrote none of the work, reads the opinion itself and tests whether it supports the claim it is cited for. Uncertain results stay visible instead of being smoothed over.
A general AI tool will confirm an invented case if you ask it whether the case is real. HiCourt never asks: it looks the case up.