Which navigation version???

I need to get a new navigation DVD for my A4. Looking on eBay, there is a significant price difference between the older versions (04,06
etc) and the latest version. Mine was an 04 version and was fine - there was only one road we have come across so far that is not on it.
Road updates aside, does anyone know if there are any other differences between the versions - i.e. are there functional updates too? e.g. one annoying thing was that it did not do full postcode searching has this been added?
Any help appreciated
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