Dotmit, I'm really not defending the iDrive satnav here as I think we all know that it's pretty poor and should be a lot better but it is very rare that a 7 digit postcode will refer to just one building, unless it is one massive building in central London!! Half a street will often share the same postcode. On my TomTom, after I've entered the full postcode it will then give me all the house numbers and/or building names within that postcode to choose from. As I said, I'm not defending the iDrive satnav and find it crazy that it can't take full postcodes.
As for the updated disc, I'm going to get one too as mine still has the original one from new so there have been a few times when it's got me down as driving through fields!