Editing home screens is a tricky business. If there is a small typo in the home screen syntax then it will not show up on the home screen control panel list. I have always made minor mistakes when using the editor on the mobile device.
I usually like to edit it on the PC. To verify if the XML tags are proper, I open the XML in the desktop IE. If the file shows up then it is guaranteed to show up in the Windows Mobile home screen list.
Or the next time you run into this problem (after editing the XML on the mobile device), copy the edited file to the desktop. And try to open the file in the desktop IE.