0 CDF would mean "it's impossible to find a block with this amount of work". That would be true only with 0 work done. Even with just 1 proof of work accepted by the pool there is a chance it will create a block, so that's not 0% CDF. If you found a block, then the round is not 0 CDF, per definition.

100% CDF would mean "with this amount of work you are absolutely certain to find a block". But that is never true. Unlike a lottery where you would perhaps be able to buy all the tickets, you can't do that in bitcoin.

As time approaches infinity, CDF approaches 100%. But just like time never reaches infinity, CDF can never be 100%.