Starting in 2008 Hot Wheels began using base codes. These base codes can be interpreted as follows.

Letters = Year of Manufacture

A	2008
B	2009
C	2010
D	2011

Numbers = Week of the year

1-52	Week Of the Year

Example #1: B12, B indicates the car was manufactured in 2009. 12 being the 12th week of the year puts the production date approximately the end of March.

Example #2: C47, which consists by a foremost transport aircraft, the Dakota or Skytrain.

Other then helping to search for new variations, These base codes have little meaning among collectors.