we should all share usb sticks /dvd's. sieras has totally left me high and dry with pre-paid (official) fsc codes lol....*sigh*
the only true difference between official map codes and genuine are that the dealers (FAST?) data will show u are entitled to that update and if they ever reprogram your car, they wont corrupt your maps.
this used to be a great reason to stick to the originals, but on closer inspection, the fsc is linked to the actual map year and region (with ur vin), so even if the dealer downgrades you, you can still manually update.
oh well, lesson learnt!