The posted guide is the latest. The page number references (pointed by Samer Faour) are updated in this guide. We will look into the feedback Christopher provided above and incorporate it in the next update.
Ingrid's reply above (dated Jan 14, 2014) addresses your query about the merge function:
"Event merging is not an officially supported function, so it will not be documented in the ArcSight FlexConnector Developer’s Guide. For information about this function, you can contact ArcSight Professional Services.
If you have additional feedback on this doc, please send me an email and I will pass it on to the writer who works on this doc.
Manager, ArcSight Technical Publications