EntityProperty.GetValue(object entityBase, EntityVersion version) doesn't return original version

It should probably be considered a bug that GetValue() returns anything for a scalar navigation property. We don't really attempt to keep track of original values for properties that aren't part of the core entity. If the property happened to be a generated one representing an entity related many-to-many, keeping up with that information would be an especially complex affair.

But assuming the property represents an entity related in a one-to-many or one-to-one association, you can get at what you want by using the EntityProperty for the associated foreign key (e.g., HeadPerson_fk_InternalIdEntityProperty). Since that foreign key is part of the core entity, we do keep a copy of its original value.