Marks the Fat Man as a unique weapon that can be found in Quarry Junction and on prospectors when it can actually be bought and found in a few other places like at the Gun Runners and at Nellis Air Force Base.
The section is an excerpt from Fallout 3 Official Game Guide regarding AP which was also incorrect.
It is actually given as a reward by Red Lucy in the Thorn, after completing the quest Bleed Me Dry. The hardcover Collector's Edition includes 32 additional pages which include concept art and faction/setting information. Hodgson, who also authored the Fallout 3 Official Game Guide.