I'm replying Dan's original message. I tend to collect the daily digests and go back to them every few days so I am seeing Dan's message and the replies all anew. Thanks to Bob, Tony, and Bill for their succinct and well reasoned answers. Also, thanks to Tony for his blog posting. I'll add my two cents.
The Reference Manuals are intended to be something that sits on the workbench or desktop and is a quick go-to reference to understand the basics about major prototypes. What was the major house cars type on the Central Vermont? It's in there.
Conversely, as great as the images in the FOFC series are, they are completely governed by what's in the collection. Coverage of prototypes was amazing, but there are gaps in terms of significant prototypes (albeit not many). If it's in the collection, it's in the books. If it's not, then it's absent. I'll refer to but not rehash the comments about the photos being intended for modeling, hence the detail shots are incredible fodder for us. Also, except in rare instances (no other photo of the prototype exists or a detail cannot be referenced any other way) the FOFC images will not appear anywhere else.
If anyone has more questions, I'm happy to answer.