@Steve and others - here are the values you can use to validate successful preparation of Active Directory. I'm working to get this information updated in the topic ASAP.
In the Configuration naming context, verify that the msExchProductId property in the CN=<your organization>,CN=Microsoft Exchange,CN=Services,CN=Configuration,DC=<domain> container is set to 15.00.620.029.
Note: If the msExchProductId property is set to 15.00.620.029, Active Directory has been successfully prepared. You don’t need to check any of remaining values in this list. The information below is for information purposes only and for those who separate the PrepareSchema and PrepareAD steps.
In the Schema naming context, verify that the rangeUpper property on ms-Exch-Schema-Verision-Pt is set to 15254.
In the Configuration naming context, verify that the objectVersion property in the CN=<your organization>,CN=Microsoft Exchange,CN=Services,CN=Configuration,DC=<domain> container is set to 15614.
In the Default naming context, verify that the objectVersion property in the Microsoft Exchange System Objects container under DC=<root domain is set to 13236.