Complete update files are always all inclusive so you do not need to install prior updates.  Patches are different.  A PATCH file (such as the SP1 for the January update) requires that the prerequisite update be installed first.
 
Updates go through the process of comparing your data dictionary to the current data dictionary and create any needed new files and add indexes or fields to existing files as needed based on the comparison.  Patches are simply an unzip of newer program files to the EVOERP or DBAMFG folder and no data structure update is performed because it was already done when the prerequisite update was installed.  The update page on the website will not allow you to download a patch if you have not already downloaded the prerequisite full update file but we have no way to determine whether you have in fact installed the update, only that you have downloaded it.
 
Not sure why (phases of the moon maybe) but we have had several instances this week of the January 2011 SP1 installed on top of the October 2010 update meaning somebody downloaded the January 2011 update but never installed it, then downloaded and installed the SP1 for the January update.  Word to the wise - Do not download an update until you are ready to install it....