Was every Roman legionary equipped with lorica segmentata in a unit (e.g. cohort), or was diversity of gear allowed?

by PETApitaS

I was playing Total War: Rome II and the question popped into my head.

Naturally during the Principate

cohort, century, legion, etc

PETApitaS

follow-up: how widespread was the use of lorica segmentata during that period?