A previous thread mentions the ability to "downgrade" from say Oracle9i to 8i by taking the 8i New Features exam. Nowhere does Oracle mention this ability on their website. I decided to ask my contact at Oracle University; he manages the OCP Program. Here's my question to him, and his answer:

QUESTION:
Imagine this:Joe Blow wants to get certified as an Oracle9i DBA. He takes all 4 exams within the Oracle9i DBA OCP Track. He's now an Oracle9i OCP. His boss then says, "Joe, that's great...but all our databases are still Oracle8i. I wish you had gotten Oracle8i certified instead."Joe then goes and takes the Oracle8i New Features exam and passes. Is Joe now Oracle8i AND Oracle9i certified?

ANSWER:
Got it, and no, we're not really set up for that. The New Features exam covers material that is different between Oracle 8 and Oracle 8i. It is built for the audience of DBAs with experience, coming off Oracle 8.

What we would do in this case is show that being certified on Oracle9i includes the context of what you would be certified on with Oracle8i, and only adds to it. All our tracks are, for the most part, this way. Ofcourse there are new tuning practices and methodologies, and new features that make things easier with newer releases. The longer procedures that might be required with earlier versions would not be covered in the 9i content.