Jockey Micro 3 In What Year Did The Kentucky Derby Start Restricting The Field To 20 Horses With The Top Earnings?

In what year did the Kentucky Derby start restricting the field to 20 horses with the top earnings? - jockey micro 3

Moreover, profit is the only horse at the age of 3 years of age or income includes only horse to earn 2-years and 3 years average age? Do other races of the owners of the Triple Crown to limit the benefits? Or are the Preakness and Belmont area in general so small that not necessary?

In addition, the program runs, a B, has horse blinders on, but what the B and F mean?

I know that the Jockey Club requires that all racehorses are tattooed on his lower lip as identification. If the Jockey Club, including the use of microchips?

Finally, some sources list 1892 Alonzo Clayton and James Perkins in 1895, when the riders younger than 15 years to win the Derby. Other sources list only Clayton as the youngest to win. Any clarificationtion on this subject?

Thank you very much.