Shouldn’t be a surprise to anyone that the lottery was mismanaged. Everything else about the Vietnam war was either mismanaged or was a lie, probably both.

TL;DR: The draft process for WWII in America involved writing dates on slips of paper and putting them into "capsules". The capsules were supposed to be randomly drawn and the order the dates were drawn determined the order men were drafted based on their date of birth. It appears, however, that the capsules were not mixed enough and so dates earlier in the year came up sooner in the draw.