SQL Server Version - are hotfixes for previous versions implied?
All hotfixes are cumulative unless otherwise stated.

Random pick, http://support.microsoft.com/?Kbid=971409


  Because the builds are cumulative, each new fix release contains all the hotfixes and all the security fixes that were included with the previous SQL Server 2005 fix release. Microsoft recommends that you consider applying the most recent fix release that contains this hotfix.


The "otherwise stated" is like these examples where you have some dependencies (sorry. bit old, for SQL Server 2000 and SP4). http://support.microsoft.com/?Kbid=941203 and http://support.microsoft.com/kb/959420