Generally the testing of any data base is done with major version during the pega product release that's the reason it confirms about Oracle 12C only and it doesn't confirm about the minor version 12.2 officially. May be you can perform the testing at lower environment to see how it behaves before you migrate to this version.
You differentiate between Oracle 11gR1 (11.1) and 11gR2 (11.2) in the platform guide. Why is it different for 12cR1 (12.1) and 12cR2 (12.2)? This is a major release, not a minor one, and saying "12c" really doesn't mean anything specific.