I wouldn't focus excessively on the "course codes". If I remember correctly, DO stands for DevOps (mostly OpenShift and Ansible courses), while AD is likely "Application Development" (and covers products such as Fuse, JBoss), etc. There are also further codes like RH (for RHEL), CL (Cloud- I believe this is just OpenStack courses), TL (Transformational Learning- not about products, but practices such as Site Reliability Engineering).
There's a huge catalog of courses, and it can be difficult to find your way around. But other than looking at the code, most pages that list our courses have filters by product, audience, etc.
For example, on:
https://www.redhat.com/en/services/training/all-courses-exams
You can filter by product, for example- and if you filter by OpenShift you will get mostly DO courses, but also an AD course. Hopefully these filters will help you locate quickly courses that are interesting for you.
If you already have a subscription, ROL has even more filtering abilities:
https://rol.redhat.com/rol/app/catalog
Hope that helps,
Álex
