How difficult is it to collect obd commands ?Will it be different for different brands?

OBD is something very interesting I found these days.Thanks to this repo https://github.com/pires/obd-java-api & wikipedia which provides the basic information of PIDs.But there is a lot of details missing like when the fault is in air bags it is left unidentified.

1. Some sources are saying that there are hundreds of more commands that helps to fetch more information about vehicle status from different sensors.How can I access them ,are they segregated brandwise?
2. Recently I came across a command 1800FF00 still I wonder which mode(service) it faults into(010C indicates mode 1).

It could be great if you share any docs that helps in exploring the vehicle diagnostics more.