Perhaps try thinking about it more in terms of inaccessibility rather than unknowability, because the latter might be creating some recursive confusion here.

> A truth that can never be known, though, is an assumption.

The real assumption, then, is correspondence. For example, it's not assumptive for me to discard a theory of fnördianism (where fnörd is a property of claims). That is because fnörd would something incomprehensible and I have no reason to believe that some creature out there comprehends fnörd. Why would I?

This example aligns more with arguments on correspondence being incoherent. If we wanted this example to get closer to deflationism, we'd associate fnörd one-to-one with some other property. Argument remains.

> I think dismissing the value of truth “because we cannot know it”

Then what is the value of a metaphysical correspondent truth, if we cannot speak of it meaningfully?

Good explanation, I agree.

If you were to switch out correspondence with deflationism, OP's comment on "conflation of a claim’s between being true and being known to be true" would become more accurate. And a criticism of correspondence is the beginning of getting to deflationatism, and is the path that Blackburn takes. Though of course you could instead also reach some epistemic theory of truth.

If there is no way to differentiate the two, then no meaningful distinction can be expressed. Your comment provides no response to this and continues off the challenged premises.

You wanting a term is not an argument in this context. There is a difference between simple practical speech and philosophical terminology dealing with concepts such as truth. So much recognizes Blackburn himself.