There is not of any article which be define it about live update of sep client.
I have found one old thread where chetan is mention it
https://www-secure.symantec.com/connect/forums/sep-121-client-computerthere-no-liveupdate-33-programs-and-features
Check this article live update difference as well
Few differences between SEP 11 Enterprise Edition and SEP 12.1 Enterprise Edition
https://www-secure.symantec.com/connect/articles/few-differences-between-sep-11-enterprise-edition-and-sep-121-enterprise-edition
Hope it help you