[...] present perfect + "yet" is basically the same as "until now". I hope that makes sense.
"Yet" and "until now" do not actually have the same meaning, nor are they interchangeable. If you replace one with the other, then you significantly change the meaning of the sentence.
If something has not happened yet, then at the moment of speaking, it has still not happened. Maybe it will happen in the next minute, the next year, in a few decades, maybe never -- all that
yet signifies is that up to and including this particular moment in time, whatever it is the speaker is talking about has not happened. The situation now is the same as it was before.
If something has not happened until now, then it has now happened.
Until now means that the situation is different now, at the moment of speaking, than it was before. You can replace "until" with "before" and still have the same meaning.
For example:
-
Its success has not been proven yet. = The success is still not proven, but there is an implication that it may be proven at some future point. (As opposed to "Its success
will not be proven.")
-
Its success has not been proven until now. = The success had not been proven before, but something has just happened or is about to happen to make the speaker confident the success has been proven now.