When you run the script mentioned here (to updated a Server Core 2008 install), you’ll see a part of the output called “Installation Results.”  In the infinite wisdom of Microsoft, they don’t seem to feel the need to plainly document these results.  They have instead included a number (1-3) to indicate the results of the installation.  Here are these codes in case you’re looking:

Exit Codes:
0 = scripting failure
1 = error obtaining or installing updates
2 = installation successful, no further updates to install
3 = reboot needed; rerun script after reboot

More here.