It didn't take long after writing the entry below about Barnes & Noble to find a further example of a company failing to effectively make its data quality initiative(s) continuous.
DHL has a list of country codes and postal code formats here.
Apart from missing a number of countries which have recently (and not so recently) created postal code systems, the list still contains Serbia and Montenegro, a country that hasn't existed since 2006;
it has the pre-1999 postal code format for Argentina, and the pre 2006/2007 formats for Armenia and Malta.
Postal code and addressing systems change at a surprisingly speedy rate, and information resources such as this one from DHL decay over time if they are not maintained. I don't know whether DHL's systems expect the same formats as are listed in this document (which I acknowledge has been posted on the Singaporean DHL site and may simply have been overlooked), but it would be, to say the least, commercially damaging if they did.