Welcome to the Ranch.
The OCPJP (1Z0-851) is for experienced
Java programmers
testing the syntax, API, OO concepts. The OCA (1Z0-850) is for junior programmers and managers testing OO concepts, Java SE API, Java EE tech, simple syntax, client/server tech.
OCPJP v5/v6 does not need OCA v5/v6.