It IS all in the interpretation.
In the 80s "wicked" was defined in the Witchtower as anybody who was of no use to jehovah and his organization.
Argument was that in noah's day the vast majority were nice people who did not like the state of the world, yet made no effort to join Noah and his fambly.
Incorrigible simply means "not to be corrected" (by the lies spouted by the Witchtower).
So witlesses know exactly what is being said, but worldlings will be conned into thinking the Dubs are not as merciless as they thought.
Nor should we forget that a very recent rag on Malachi 4:1 said that "neither root nor branch will be left" proves that God will destroy the babies of non-believers.
HB