The F-19 was what people speculated the rumored "stealth fighter" would be named. There had been rumors for years, but the public didn't see it for the first time until 1988.

In Tom Clancy's book Red Storm Rising, about a hypothetical Third World War in Europe, he conceives of it as something like the F-35 ended up becoming -- a stealthy multirole aircraft (fighter-bomber). They called it the "F-19 Frisbee". The 19 comes from the fact that the previous fighter designation was for the F-18 Hornet.

I am fairly confident the f-19 was the f-117, fueled by aviation journalists wild imaginations, probably based on early speculative concepts.

Or if you are more conspiracy minded a deliberate misinformation campaign to further obscure what the nighthawk was and was not. this conspiracy is reinforced by the f-117 designation itself. They used a century-series number(this series of numbers had been phased out for quite some time at this point) and an F(fighter) designation for something that is effectively a light bomber.

That being said, I wonder what the actual f-19 was? The missing numbers always interest me. f-17? f-19? f-20(tigershark?) f-21? f-24:24? (i think I read somewhere the last gap was marketing sigh)