Perhaps they meant to say that 1 in 220 professional authors will make it onto one of the 42 top ten lists at some point in their lifetime. They could have reached this conclusion by calculating 52x42x10=21,840 available slots and then divide that by the average length of time a book stays in the slot, then multiply by estimated lifespan after writing your first book, and compare that to the number of published authors in the world.
If you estimate 10,000,000 published authors who each wrote their first book at age 18 and live to be 72, that’s a professional lifespan of 54 years. If we assume that each book spends an average of six months (26 weeks) on one of the lists, then the number of books that make it onto a list during any 54-year period is 54x21,840/26 = 45,360. That number doesn’t sound crazy to me at all, might even be realistic. Compare that to 10,000,000 published authors and you get almost exactly 1 chance in 220.
Now, I’m assuming just one book per author but it works equally well if you merely assume that the author in question writes the same number of books as an average author writes.
I think this passes the sniff test. With 10 million contestants competing for 21,840 slots, each contestant has 1 chance in 220 of getting a slot at least once in 54 years (assuming that once you get picked you stay on the list for six months).
This makes a kind of sense. If you try out for Jeopardy you have a 0.4% chance of making onto the show. If you write a book and get it published, you have 1 chance in 220 that you will make it onto one of the NY Times bestseller lists during your lifetime. If you don’t write a book and get it published, you have the same chance as someone who never tries out for Jeopardy at all. zero.