"Kennan an Sich" is the necessary corollary to "Ding an Sich". KaS is all that is known to us, all that we believe that we know, as distinct from the reality beyond our senses, instruments, minds, and computations. An estimate of the total human population currently falls within KaS, but the actual population is currently beyond our ability to measure, and therefore falls within DaS.
Allow me to tell a narrative, perhaps? Imagine that you are drawing a map of the entirety of Mankind's collective knowledge (the "Kennen an Sich"). It'll have to be drawn in three or more dimensions, but I only have to describe it roughly, so here goes.
We begin with a Koch snowflake, and use it as an analogy, with the perimeter being the Lived Experience, the boundary between the Ding an Sich and the Kennen an Sich. Any move closer to the center is a form of idealization or abstraction, while a move toward the perimeter is a form of application or pragmatism. Having covered two dimensions, we have a wide variety of choices for the third. We could choose time, and then discuss resconstructions of history and projections into the future. We could choose elegance of theory, confidence, complexity, coherence of the global will, or a near-infinite variety of other measures. It all depends really, on our intentional stance and the results we're looking to achieve in what area. P:D