Hey Lily,
When we build an update from a specific version we get a seemingly valid server and update files to all of the version from that version onward , but when we run the WyUpdate it fails to update throwing that it needs to download the full version file (which we intentionally didn't upload in order to test the version specific update) .
It sounds like a file is failing to patch. Why? Because the version installed on the customer's machine (your test machine in this case) doesn't match the file in the version in wyBuild.
You can see exactly which file is failing to patch by unchecking the "Create a catch-all update" checkbox (File -> Properties -> Update & servers files). Rebuild your updates. Re-upload them to your servers.
Then re-run wyUpdate and you'll see why the file is failing to patch.
Tell me if that helps.