With the winzip commandline addon, you can use the
Unzip only newer files. This option updates existing files if the archived file is newer and creates new ones if they do not already exist.
wzunzip -n "c:\my documents\spring2007.zip" c:\semesters\spring05
This example will extract, from c:\my documents\spring2007.zip, ONLY those files that are newer than the files that currently exist in c:\semesters\spring05 OR that do not already exist in the c:\semesters\spring05 folder.
You might want to combine it with the
-o option - "Overwrite existing files without a prompt (automatically reply "Yes" to each overwrite prompt)."