1. There are generational athletes but in every instance that I remember, there was a hint and foreshadowing. Someone else can find different instances but I am working from memory. There are records that stand for a long time, but Bob Beamon events don't really happen in swimming because unlike the perfect leap with timing, spring and speed coming together simultaneously, swimming requires aerobic and anaerobic factors where freak sequence of timing won't produce the freak time.

2. Mark Spitz 1972 was a generational moment. But that moment was foreshadowed in 68 in Mexico City, where his gold medal haul didn't occur. He was a young 18 year old in 68 but a seasoned vet and the best in the world regularly in 72. He hit is on all cylinders.

He 200m Fly was generational but now would be considered sub ordinary. The women are approaching that time a 2:00.7. He won by many lengths. Here is a video of it. https://www.youtube.com/watch?v=IF3kIvu7PZM

3. Janet Evans was so much better she routinely trounced the distance women as does Ledecky.

We can go back to the sprints and see Pan's progression is nonsensical and when I have more time, I'll show the progression of the 100m Free time. It doesn't occur with 19 year olds. It occurs with 21 plus year olds. https://en.wikipedia.org/wiki/World_record_progression_100_metres_freestyle

Pan just magically appeared out of the Chinese chemical factory in one of the most competitive distances and blows everyone else away?