Detect SqlNotificationRequest failure in .Net?

Question

Periodically SqlNotificationRequest fails to register a SQL query notification subscription (sys.dm_qn_subscriptions is an empty set).  There doesn't appear to be a way to look up the UserData in the subscriptions table to verify that the request registered a notification subscription.  How is this done?

                        var request = new SqlNotificationRequest
                        {
                            UserData = registrationKey.ToString(),
                            Options = options,
                            Timeout = MAX_REQUEST_TIMEOUT_SECONDS
                        };

                        using (var dependencyConnection = new SqlConnection(connectionString))
                        {
                            dependencyConnection.Open();

                            using (var dependencyCmd = new SqlCommand(myquery, dependencyConnection))
                            {
                                dependencyCmd.CommandTimeout = MAX_REQUEST_TIMEOUT_SECONDS;
                                dependencyCmd.Notification = request;

                                using (var reader = dependencyCmd.ExecuteReader())
                                { // data is returned but there is no subscription