How do you know if monitor has a 1:1 ratio?

That is not a standard spec that is listed. You might be able to find it on some manufacturer's websites, though.

However, it should be noted that the Nvidia video card drivers can force 1:1 mode.

Has it been your experience that this *always* works, or are there monitors upon which it doesn't?
Well, up to today, I would have said that it should always work, but as I was writing my post earlier, I got to thinking. What if the Nvidia control panel is relying on the monitor's native ability to do 1:1? There was somebody on this forum, earlier, that couldn't even find a 1:1 ratio option in the Nvidia control panel. If it is relying on the monitor, then it would not be able to do 1:1 on all monitors.
I don't know what the answer is... though it is probably more likely that the drivers can force 1:1 on any monitor. Technically, it should be possible to program the drivers to force 1:1 on any monitor, no matter what. Whether Nvidia programmed the drivers to do it that way, I don't know.