Don't we all leave stuff out when we write -- and aren't others grateful? Shall I take pains in this response to include every critical nuance? Would I have time to write it or you to read it?
Then I think another aspect of your argument may be a kind of circularity. Did they KNOW that their writings were going to be put into something called the Bible? Did they each know what the other one was going to write ("Okay Matt, you, Mark and Luke do the last supper, we'll let John do the foot-washing, the farewell discourse and high priestly prayer, and the Bread of Life stuff. Okay? Anything we're leaving out?)
In other words, full blown sola scriptura would require, almost by definition, that nothing was left out. But we can't use it to prove to someone who doesn't believe in it that nothing was left out because the Apostles wouldn't do that.
Is that at all clear? Weren't we talking about the Eucharist here?
Since their writings were divinely inspired they would not have to know.