Even though all the information required, like country, country/postal code, country/state/zip code, might be present, is important to consider what happens if any of these items is entered incorrectly by the customer. What it's certain is that you'll get and empty rate table as a result, as a result of the shipping API sending back an error message. I was handling it by clearing the customer's shipping meta info in order to bail, so maybe something else could be implemented based on the modifications currently being worked on.