Hi, I think the latest version of the Portal API is 2.2, because it's referenced in IBM's Deprecated List -
http://www7b.boulder.ibm.com/wsdd/zones/portal/portlet/4.1api/deprecated-list.html - and you can access the more recent API from that link as well.
The other place that has decent documentation for Portlet Development is in the InfoCenter for the enable version -
http://www7b.software.ibm.com/wsdd/zones/portal/V41InfoCenter/InfoCenter/wpf-ena/en/InfoCenter/index.html, Developing Portlets. I don't know how it differs from the guide you use, but enable is the level from which the certification exam derives, so it certainly couldn't hurt. Sorry I couldn't be more helpful, but the IBM site is a nightmare for finding for documentation, as you probably know.