Hajime No Ippo isnt an accurate representation of boxing man.
They model their fighters on real life people and all the fights have...to an extent...happened before.

As for the flicker jab...well...it isnt "real" in the sense that no one calls it that.
Its just a jab from the hip. But their arent any real reasons why you would want to use it unless you were over 6 feet tall and had really lanky arms.

Nuff said.

I think its an impractical technique anyway.

Sawamura's berettas are far more effective