The current system has confused a lot of people as each March reg happens to be the same as the year; 02 for 2002, 03 for 2003, etc.
Don't forget that the two digits are actually separate. The first digit of the reg is refering to the 6 month period (what used to be 0 for Mar - Aug will now be 1 and Sep - Feb will now be 6 instead of 5). The second digit of the reg refers to the year. 0 being 2010, 1 for 2011 and so on. So, as Buenchico says, the next reg out in Sep 2010 will be 60.
Therefore, Mar - Aug 2020 will be 20 and Sep - Feb will be 70.
This system allows for 50 years worth of registration years; up to 99 for Sep 2049 (had it started at 00 in Mar 2000.)
The previous two letter based systems only allowed for 21 years each (I, O, Q, U and Z being omitted).