vin,serial,production number questions

[Spartan]

I was curious. i have looked at my numbers plenty of times. i went to look at the pillar plate and noticed my serial number is really high so i started wondering if the are numbers stating production of trucks in 69 - how many total. Also on the plate at the bottom is "DD"... thats not in the decoder! ideas?
and finally is there a way to tell what month th truck was built? via the serial number? AFAIK its 824,313 which would make it the 724312th truck built?
I must be reading something wrong?

Any help would be great. Im thinking about some old plates I have laying around and thinking maybe if the month matches the truck that would be "Extra Special" (church lady)

thanks again
Nim