Re: Ranking systems in different countries
Is the six monthly grading exclusive of any minimum 'mat time' requirement? Most associations require at least 100 sessions (often more) between first kyu and shodan. Based on this with twice a week training excluding closures for national holidays and shut downs it would be a year between grades. If you can just rock up every six months and pass a grade with minimal practise, I think there are bigger issues here and yes three years to shodan is too fast ... But if you put the time in and are technically ready and mature enough I see no reason why you should not reach shodan in less time than 'the norm'.
In terms of having to re-grade ... depends on the club you come from and where you go.
Just enjoy your training, grades will come along when you are ready.