Once a friend who was also a Judo-ka invited me to attend a clinic his instructor from New Jersey was having at the Scranton YMCA. The instructor was a long time Judo-ka in his own right.
He explained that his Japanese instructor had waited 20 years to show him this move. It was interesting. In a clinch he pressed down one way and then reversed himself falling to his rear the opposite direction throwing my friend 20 feet the other way. He explained that his instructor choose to teach it at 20 years. Not that that was necessary, as there were plenty of white belts at that clinic and they were working on it too.
Now you can make a point that this wasn’t taught until something was reached. Whatever that was. But he was competently instructing white belts in the technique.
This seems to relate to stories that often non-American instructors (Japanese, Korean and others) did hide material. What you don’t know exists you can’t master. Reminds me of when the American TKD team attended competition in Korea and was whipped out by axe kicks for which they had no defense. Seems their instructors didn’t teach them that kick existed. Oooops.