does different arm TRM revisions also have changes in Hardware?

Hi

I have an inquiry. our company is using Cortex-A9 quad Core. So in ARM website there are many technical reference manuals for the same in different revisions , such as:

r2p0

r2p2

r3p0

r4p0

r4p1

so what should i follow?

or should i follow latest revision?

or my SOC has specific revision corresponding to Cortex -A9 implemented, if its so, how can i found it, if my SOC doc does not refers about it?