I think there is a slight difference between 0.99 and 1 or 0.999 and 1 etc…
Take an example of a system that succeeds 99.999% of the time to do whatever task and fails the remaining 1*10^-3%. This effectively means that the system will fail once every 100,000 attempts. This sounds a bit faulty since you guys are debating 0.999 and not 0.999 but a system or law of nature that succeeds 99.999% keeps that very slight possibility of failure while a 100% successful system eliminates anything other than success. This may sound stupid but there is a difference because that 0.0001% failure exits in a 99.999% successful system while the 100% leaves no margin for debate! (Failure wise)
An example of this is a quantum fluctuation whereby the possibility of you randomly chosen (by nature) to be tunneled through a concrete wall to another room exits! although very small. The very nature of that small probability existing allows me to debate it, while otherwise I wouldn’t be able to.
Another example I can think of is a trans-planetary missile that is 99.999% accurate. When launching that missile to Pluto for example, a tolerance between where it is aimed and where it will hit exists and is certain.
I have to admit that reading your posts reminded me when I got worried about birth control pills because I thought they were 99% effective (actually 99.99%) and thought the law of large numbers will get me! Hence my 1st post.