You can take this a step farther by if you have multiple ship to codes. In addition to adding the UDF in the AR customer master, you can also add it to the Ship To table. Then have your SO header UDF pull from both fields. Also, don't forget to circle back by adding the AR Invoice History Header UDF to the SO Header UDF in case you create the SO from a copy from the Invoice History. Finally, are you using this field to populate the WorldShip records?