I think it is actually correct. The geonameid for the admin division should be in the countryInfo file. The island feature code refers to an entity of type 'T' (islands, mountains, etc) wheras 'A' refers to countries etc.
the "daily" dump is a daily dump The web services are running on different servers and are normally synchronized in realtime: http://ws.geonames.org/search?q=Milandes
The postal code database and the normal GeoNames place name database are two different datasets. We are working on merging them, but as you see your self there are quite some differences and as usuayl the devil is in the details.
For the admin codes we use the most common national codes (like INSEE codes in France). The codes cannot be updated with the userinterface, I have to set them directly on the database.
The code '00' means 'not applicable' but it is often used as 'null'. This means the admincode should be unique for all exept '00' and 'null'. Administrative divisions should not have neither '00' nor 'null'.
If you want to help assigning missing admin codes then you should figure out the code from the national code system and then you can send me the code with the geonameid and I do the update.
I don't have a list. On Windows there is a package for East Asian languages that is already on the computer and only needs to be unpacked. Use a search engine to find out where exactly to click on your operating system.