you are right about the 01 is jan 02 feb and so on and 13 is back to january
the sites that i used to find this info are these about 1/2 the way down on this one
http://www.brads41-46chevys.com/id14.html and this one about 2/3 of the way down
http://www.vehiclesofvictory.com/Chevy%20Specifications.htm rh
