"Administrators guide" section missing in Latest update

I need to learn OpenShift in an Administrators context by referring to official docs over OpenShift website. There are PLENTY of Documentation versions in the official website and here is my confusion:

If we refer the 3.11 documentation of OpenShift, its has a very useful Administrator guide section as in the link below;

https://docs.openshift.com/container-platform/3.11/admin_guide/index.html

But this Section is entirely missing in the latest 4.12 version of docs as in the below link;

https://docs.openshift.com/container-platform/4.12/welcome/index.html

Although 3.11 has become older version BUT its Administrator's guide is very vital and needed. Why is it missing in the latest 4.12 documentation ? It should be there. Also the left side format of the documentation titles is also changed in various versions of Documentation. Can we still use the 3.11 guide to study.

A guidance by an OpenShift expert would be helpful here.