Where Did Nick Valentine Get This Info From? (The Mysterious Stranger's Presence During FO1)

In Nick Valentine's office, under his bed there's a case file detailing his investigation on The Mysterious Stranger, starting from his looks, to theorizing who he is, to reports of where he's been seen over the years dating all the way back to the events of Fallout 1. (As you can see pictured above.)
Pretty cool nod to FO1 right? Well other than being a "cool nod", arises a very important and valid question of... WHERE THE HECK DID NICK VALENTINE GET THIS INFORMATION FROM!?
Seriously, how does he know about The Mysterious Stranger being present on the West Coast? PLUS! How does he even know about those specific sightings that happened around 46 years ago(Fallout 2's events) and 126 years ago? How? No really HOW!? Is he REALLY that good of a detective to get this kind of info? Or was he told by somebody who was making this stuff up on the fly, but had no clue that what they were saying WASN'T so far from the truth?

These are the kind of questions that make me think how can Bethesda NOT think of these kind of things through, if they're going to do a pretty significant nod to the older games such as this!?

 

A bit unrelated to the questions in this thread, uh I made a compilation of The Mysterious Stranger's appearances throughout the Fallout series, based on those sightings listed in Nick Valentine's case file on him.
(pictured above)

 

Thanks man!!! And yeah, I do my best to keep things interesting and entertaining on here.