No, a holodisc that could be propoganda crap says it, and another piece of in game info contradicts it. And logic makes it look ridiculous. And ya, the mighty Vault Experiment. But for not saving people, they sure did a good job, as many people you meet, came from a vault. My ancestors came from a vault. My parents came from a vault. I came from a vault. States are different fyi in FO NCR than real world. There is a mystery 650K people. That makes NO sense.
While it's not spit out like in the case of TES people forget propaganda exists in the FO world at times. False info can be gotten if you depend on a single source. Some more obvious than others, by FO2 if not 1 most knew the government was clearly lying to the populace. And this exists after the War as well from the outlying communities.
Fallout 2 is a game I place mistrust on because Avellone and Co. put a deft of errors not to mention the Fallout Bible(Not to the extent of discounting it as canon. 3 is canon too. And obviously if Bethesda wanted to they have the right to retcon all existing lore other than FO1.)
While I always believed more in VC's numbers by New Vegas it seems NCR's early propaganda was true about the 700k+ number. It's canon as per Obsidian.
But is it viable? In my opinion by FO2 I'd believe more in around the 200-400k range. People seem to undermine exactly how strong the nuclear launches and yields were, although so do the FO games. And we don't have a true frame of reference to know how it'd go in our world when it's taken thousands of years for the natural world to get very little shift in state it's in currently.
I do think 2 and NV boosted the growth rate even for a relatively unscathed vs the East part of the U.S. but I can see in the course of wanting each game to be interesting the need for it.
It undermines how blistered 1 set the world as but it seems due to largely everyone but the core team being involved in games after, the nuclear arsenal launched isn't as destructive as you'd expect, thus the very high survival rate than you'd expect.
Of coarse this is why factions like House and Legion are introduced, or atleast the lesser thought reasons. Having a 3 million+ nation with a strong army continue further would very much continue on a predictable course and repeat to the nation that was.
And finally, the games themselves can't fully present populations either. Worlds created in games like FO or others obviously have more people but as a game you can't have or afford thousands of NPCs per city to speak to.