Hi Brian,
Thank you for the sharing the post. I just thought I would share some findings that others may find useful.
Looking a little further into the issue we're experiencing with an upgrade from Project Server 2010 to 2019 that started life as Project Server 2007, I can confirm that in Project Server 2007 the default Enterprise Global GUID is 5850E0F8-CDF2-4092-9CC3-577102564A24. I have just built a new Project Server 2007 environment to confirm the default Enterprise Global GUID.
It would appear that in later releases of Project Server, the default and expected Enterprise Global GUID is 75CDD7DB-1B68-4B70-A8D6-2FE52DA83ACD as mentioned in the post. When upgrading to Project Server 2019 from Project Server 2007 you will find that the Enterprise Global can't be opened. By changing the GUID to 75CDD7DB-1B68-4B70-A8D6-2FE52DA83ACD, you will be left with a blank Enterprise Global.
Thank you
Lee