jakie62 very cleverly figures out when a globe was manufactured based upon historical map changes that took place over specific periods of time. Using information that includes the names of countries, under what government they reported, and the effect of war, he is able to pinpoint the exact date of the globe with few exceptions.
While he knows a lot of the geographical information by heart, jakie62 readily admits that he uses outside sources for information.
I know a lot off by heart and can get a globe down to a 2-5 year range on my own, but I usually have to use Google to get it narrower than that.
via Andy Baio
