The AI_MISSING_PREREQS property will only be set if at least one of the "Pre-Install" prerequisites was scheduled for installation (Important note: scheduled for installation, not successfully installed), otherwise the property is empty.
If you want to use this property to condition the "WelcomeDlg", you can go to "Table Editor" page --> "InstallUISequence" --> "WelcomeDlg" --> "Condition" field.
The above solution requires an Enterprise suite or above.