How come SQL Prompt doesn't flag Invalid Synonyms in the 'Find Invalid Objects' routine

SELECT DB_NAME() AS DBName, Name AS Synonym, base_object_name AS RefersTo, 'DROP SYNONYM ' + SCHEMA_NAME( schema_id) + '.' + Name + ';' AS FixFROM sys.synonymsWHERE DB_ID( PARSENAME( base_object_name, 3 ) ) IS NULLORDER BY Name;