Hi,
CodePlex has been shut down completely on December 15th, 2017. Most of the documents have been migrated to GitHub as per the author.
https://devblogs.microsoft.com/bharry/shutting-down-codeplex/
For example, below topic on CodePlex marks a notification to users redirecting them to the new link in GitHub
https://archive.codeplex.com/?p=wsuspackagepublisher
However, on the page you required, there is no such redirecting information, which means the project was not be migrated to any new place. Since CodePlex is totally shut down, there is no other way to find the original documents.
But you can have a try to search WSUS related topics in GitHub. Maybe there will be some useful information for you.
https://github.com/explore
Hope the information can give you some help.
Thanks,
Eleven
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