I am confused about the diode names; the model names on the documentation website does not seem to match with the one in the xschem setup of the latest open_pdk release. For example, a grep for ndiode gets no results on any of the files under libs.tech/xschem. What is systematic about the diode model naming currently used in the spice model files ?

Yes, that documentation is definitely wrong. Please file an issue with the github issue tracker on https://github.com/google/skywater-pdk and call out @User specifically.

@User: https://github.com/google/skywater-pdk/issues/352