I would say that the limit isn't when the ding an sich is discovered; but, comes even before then. In other words, it isn't a known unknown; but, rather an unknown unknown. Even that what we think we know about can be an unknown known about the ding an sich.

Small point, made by Lewis White Beck in one of his prefaces. Kant rarely uses the expression ding an sich. It is more usually ding an sich selbst, translated by White as, thing in itself as it is in itself.

A distinction that makes a difference, rather like the distinction between, "money is the root of all evil," and the correct, "the love of money...".

Insisting on ding an sich, it seems to me, cuts perception out of the picture. which the selbst preserves.

There are two views, it seems, in Kant interpretation on the question of the status of the thing-in-itself. One sees the thing-in-itself as a positively existing metaphysical entity, about which we have no knowledge. Another sees the thing-in-itself, not as pointing to some metaphysical entity, but as a limiting concept, or a term used to refer to the boundary of our knowledge of the world. Kant may distinguish between a limit and a boundary, but I don't know what bearing it might have in determining what the thing-in-itself is.

These two views are related to whether one views Kant as a one-world or a two-world theorist.

These two views are related to whether one views Kant as a one-world or a two-world theorist. — Thorongil

(Y)

I think this 'one-world/ two world' distinction fails because even if the thing-in-itself is understood to be, in the so-called "one-world" sense, merely a boundary of our knowledge of the world, then that would still entail that there is a world of our knowledge, and the world that lies beyond our knowledge: which really amounts to the same thing as there being two worlds from our point of view. Of course from the "absolute" point of view there might not be two worlds, but the question seems incoherent when any attempt is made to 'consider it' in this 'context' in any case.