When you install a service pack for Windows Server 2003 or for Windows XP, some hotfixes might not migrate in the migration process at the end of the service pack installation.
When this issue occurs, you may notice that Windows Update (WU) or Windows Server Update Services (WSUS) offers you some updates that were already installed before you installed the service pack. Utilities such as Microsoft Baseline System Analyzer may report that previously installed updates are missing.
Additionally, some entries that resemble the following are written to the Svcpack.log file:
After you install the service pack, we recommend that you use Microsoft Baseline Security Analyzer or Windows Update to install any updates that may be missing. These missing updates include the updates from the failed migration and include the updates that were made available after the release of the service pack.
Migration is an operation that prevents a regression of file version numbers. It is performed when you install a service pack.When a service pack is installed, files are updated to the file version numbers of the service pack first.Then, the updates that are not included in the service pack and that were previously installed are reinstalled.