diff --git a/README.md b/README.md
index abbeda9..6d1ad08 100644
--- a/README.md
+++ b/README.md
@@ -294,18 +294,16 @@ $ ttn-lw-migrate firefly device --invalidate-keys < device_ids.txt > devices.jso
 
 The Firefly LNS does not strictly enforce device to application relationships.
 
-Setting the `--all` flag will export **all devices that are accessible by the API key** are exported.
-
-The `application` command without the `--all` flag does nothing.
+Setting the `--all` flag will export **all devices that are accessible by the API key**. The `application` command without the `--all` flag does nothing.
 
 > Note: Please be cautious while using this command as this might invalidate all the keys of all the devices.
 
-Similarly, to export all devices accessible by the API Key,
+To export all devices accessible by the API Key,
 
 ```bash
 # dry run first, verify that no errors occur
 $ ttn-lw-migrate firefly application --all --verbose > devices.json
-# export devices
+# export all devices
 $ ttn-lw-migrate firefly application --all --invalidate-keys > devices.json
 ```
 
diff --git a/pkg/export/export.go b/pkg/export/export.go
index 669d141..7a08cee 100644
--- a/pkg/export/export.go
+++ b/pkg/export/export.go
@@ -62,7 +62,7 @@ func (cfg Config) ExportDev(s source.Source, devID string) error {
 		return errDevIDExceedsMaxLength.WithAttributes("id", id)
 	}
 
-	if dev.Ids.DeviceId != oldID {
+	if dev.Ids.DeviceId != oldID && oldID != "" {
 		if dev.Attributes == nil {
 			dev.Attributes = make(map[string]string)
 		}
diff --git a/pkg/source/firefly/config.go b/pkg/source/firefly/config.go
index 8f7e801..32edfd2 100644
--- a/pkg/source/firefly/config.go
+++ b/pkg/source/firefly/config.go
@@ -48,19 +48,7 @@ type Config struct {
 // NewConfig returns a new Firefly configuration.
 func NewConfig() *Config {
 	config := &Config{
-		flags:           &pflag.FlagSet{},
-		joinEUI:         os.Getenv("JOIN_EUI"),
-		appID:           os.Getenv("APP_ID"),
-		frequencyPlanID: os.Getenv("FREQUENCY_PLAN_ID"),
-		macVersion:      os.Getenv("MAC_VERSION"),
-		invalidateKeys:  (os.Getenv("INVALIDATE_KEYS") == "true"),
-		all:             (os.Getenv("ALL") == "true"),
-		Config: client.Config{
-			Host:       os.Getenv("FIREFLY_HOST"),
-			CACertPath: os.Getenv("FIREFLY_CA_CERT_PATH"),
-			APIKey:     os.Getenv("FIREFLY_API_KEY"),
-			UseHTTP:    (os.Getenv("FIREFLY_USE_HTTP") == "true"),
-		},
+		flags: &pflag.FlagSet{},
 	}
 
 	config.flags.StringVar(&config.Host,
diff --git a/pkg/source/source.go b/pkg/source/source.go
index 2de5849..428416b 100644
--- a/pkg/source/source.go
+++ b/pkg/source/source.go
@@ -56,7 +56,7 @@ type Source interface {
 	RangeDevices(appID string, f func(s Source, devID string) error) error
 	// Close cleans up and terminates any open connections.
 	Close() error
-	// Iterator returns an iterator for devices.
+	// Iterator returns an iterator for the source.
 	Iterator(isApplication bool) iterator.Iterator
 }