A, We don't know everything but the evangelistic zeal of evolutionists here certainly contradicts that notion.....except when they have to eventually change the details of the story.
creation believers know that they don't know everything, but are upfront about their presuppositions.

Since Troubadour responded to 'B', I'll tackle 'A'.

People are people. Sometimes they get enthusiastic and express things in a way that makes them seem as if they think they are the fount of all knowledge. But when they are calm and have had a nice cup of tea you will find that what they are saying is that we are dealing with a massive amount of evidence for something on one hand, and literally zero evidence for an alternative on the other.

Then you talk about changing stories. It is in the nature of science and indeed growth of knowledge of any kind that when you learn something new you need to incorporate it into what you already know. Occasionally it will involve throwing out a chunk of what you thought you knew, but most of the time it is a slight modification in understanding. So do not say ".....except when they have to eventually change the details of the story" as if that were a problem: it is how we grow and develop either as a society or as individuals - children do it continually as they become adults. It is not a bad thing.

Not is it the case creationists are up front with their assumptions. For example, you will find that they say 'God created it' on occasions, and on others that they insist they are not invoking any notion of God, just questioning the orthodox view. This is especially the case in the US when there are constitutional restrictions on when you can use religion in a state context - "we aren't talking about religion or God, just signs of design" - and other situations where you can - "let's build an ark".

All that creationist admit to not knowing is exactly how God did it, but that God did it is not in doubt (except when the constitution prevents them saying that)