See above about canon. This from the developers who made the game about in game content, not timeline speculation.
This is the game developers saying they don't know, haven't figured out yet how big they want the NCR.
This is why two different in game documentations say conflicting things. They didn't want to commit to anything.
Basically, I find something that backs what I'm saying, and you can't accept it. Ya know, sometimes you need to think for yourself, and question authority. The 700k makes 0 sense based on FO1. Also, Shady Sands is the capital of the entire NCR, not the state of Shady Sands. Theae are city states. No doubt, the largest is the Hub or repopulated LA.
The 3K is just important when trying to figure out the entire NCR population.
You obviously played the game, if the populations of FO1 booming to 700k makes sense.. I dunno what to say. Why would 697000 other people decide to follow 3000? Lol..
Obviously, I gotta go to the Glow...