My attention was caught today by an online discussion here hosted by the English-language Vietnam News, about introducing a postal code system to Vietnam to resolve the problem of duplicate thoroughfare names within cities.
Of interest to me is that Vietnam has had a postal code system for years, updating it from a 5-digit code to a 6-digit code in 2004. Clearly, though the system has been designed, it has not been implemented to the extent of informing the residents.
This is not as unusual as you might think. Some countries - Bahrain and Nicaragua spring to mind - are coy about their postal code systems, even to the extent of requesting people not to use them because sorting continues to be done manually. I've had people from Costa Rica swear blind to me that their country has no postal code system, even after I've pointed them towards the postal website describing it. Clearly, whilst some countries are happy to design postal code systems, the expense of implementing them - mechanised sorting systems, information dissemination and so on, tends to put a brake on following the projects through.