Version numbering for Oracle Database, Enterprise Manager, and Fusion Middleware products began to change after November 2015. The new version format makes it easier to see which bundle patches are from which time-frame, and in particular which patches are from the same Critical Patch Update release.
This change is documented here:
Some bundles may continue to use a numeric 5th digit in the short term, but will transition to the new format over time.
The new format replaces the numeric fifth digit of the bundle version with a release date in the form "YYMMDD" where:
The "release date" is the release date of the main bundle / PSU / SPU. In some rare cases, for example where the same bundle is released on multiple platforms, the patch for a specific platform may not be available until some days after the "release date".