"defintions released" vs "extended version"

Could somebody tell me the difference between "defintions released" and "extended version" on this webpage here: http://www.symantec.com/security_response/definitions.jsp

For example:

Behavior-based protection says defintions released 4/10/13 and extended version 4/4/2013 rev. 11. The extended version is what is installed on my clients. When I run liveupdate on the SEPM it completes successfully saying no new updates found. I was under the impression that behavior-based protection (truscan or proactive protection) defintions are released daily. Has this changed in 12.1?

SEPM version 12.1.2015.2015

Client version 12.1.2015.2015