Given that incredible is an adjective, I'm not too clear on where it may replace extremely and very, both adverbs. Accordingly, I'm not sure whether I have even understood your question correctly, Fred.
From the OED...
"1482 Monk of Evesham 33 An inestymable and incredibulle swetenes of ioyfull conforte."
I don't really see that his "incredible sweetness" is so very different from "It was an incredible goal" despite the fact that it is over half a millennium old.
Re issue, I'd guess that the rest of us have simply taken up the legal concept in the sense of "the matter in QUESTION."