|Let's take a look at Objectivist epistemology with a few words missing.|
Objectivism says knowledge means X knowledge. They are the same thing. This is as against non-knowledge (skepticism). This is a package deal which packages together X and knowledge.
Objectivism says X is when your idea has W, Y and Z. W, Y and Z are the requirements of X.
Critical Rationalism (a name for Popperian epistemology which I'll use here) says that that W, Y and Z are requirements of knowledge, and leaves out X.
W means that no contradictions are allowed. No compromises. Not even a little. That is a requirement of knowledge. As a critical rationalist would say, one flaw or criticism is decisive.
Y means that knowledge is related to what question, problem or situation you're interested in. What is knowledge in one situation might not be very helpful in a different future situation where you know more. But it still is knowledge for that first situation; it's not invalidated.
Put another way, knowledge always address some kind of question (which critical rationalism calls a "problem") of some sort. Knowledge is, among other things, ideas with some purpose. If idea A answers question B, it will still answer it even once people are way more interested in question C. It's still knowledge, that doesn't change as you learn a better question than B and a better answer to the new question. A still answers B.
However, one must be careful. The old idea, A, still answers B, but it is invalidated in an important sense. It might be a really bad idea to use now, it might lead you to disaster; it may well be false. For example, Peikoff gives the example of blood types. First people learned about A, B and O blood types. Later they learned about positive and negative (A positive, B negative, etc). The A, B and O blood types idea is still knowledge -- it has value, it addresses the original situation well -- but if you say "these two people both have blood type A, a transfusion is safe" you'd be wrong. So the old idea still has merit, knowledge, partial truth, but it's also false. It was the best idea to use in the original situation, but should not be used now; now it's refuted for further use.
Objectivism says omniscience is not the standard of knowledge. Critical rationalism agrees. Just because an idea lacks omniscience is no reason to attack it, reject it, be agnostic, hesitate, etc... So the blood type idea wasn't omniscient, it didn't predict and address all future developments in the field, it was limited. But that doesn't disqualify it as knowledge.
Z means the idea has no rivals (currently, in this situation; the future is fluid). The current state of evidence and argument says Z is right, and nothing else is reasonable. Z addresses the question/problem/situation. No other (known) idea would. The only rational thing to do is accept Z (and be willing to use Z, act on Z, etc). There's no rational alternatives in this situation.
What words did I leave out? X = certain, certainty. W is "absolute". Y is context, contextual. Z is "conclusive".
Apart from the issue of the package deal where "certainty" is packaged in but doesn't add any value, what do you think? If you disagree, why/where? If you agree, what do you think contradicts critical rationalism?