Here's the story previously denounced as invalid all these years.

It's still invalid. It has nothing to do with NASA. There is no evidence of some gaint comet coming toward Earth. Just as there is no evidence of the notion that Aliens are visiting Earth. Or that some unseen black hole is going to eat up Earth next month. Or. Or.
This doesn't mean it's impossible that a gaint comet, aliens visits, and a black hole will at some time collide with Earth- it simply means there is no convincing evidence which supports these or an infinite amount of other possiblities.

Washington Post
Mystery Heavenly Body Discovered, a front page story
31-Dec-1983

A heavenly body possibly as large as the giant planet Jupiter and possibly so close to Earth that it would be part of this solar system has been found in the direction of the constellation Orion by an orbiting telescope aboard the U.S. infrared astronomical satellite. So mysterious is the object that astronomers do not know if it is a planet, a giant comet, a nearby "protostar" that never got hot enough to become a star...When IRAS scientists first saw the mystery body and calculated that it could be as close as 50 billion miles, there was some speculation that it might be moving toward Earth. "It's not incoming mail," Cal Tech's Neugebauer said. "I want to douse that idea with as much cold water as I can."