Potential Kennedy Half Set

Out of curiosity, I wonder if anybody can tell me how many sets of dies from each of the 4 mints used to produce the 2014 silver Kennedy half sets at the 4 mint locations were? I was told that on special mint or proof coins produced, each set of dies are removed and destroyed after minting approximately 20000 coins. Which leads me to my second question, if say 20 sets of dies are used for each coin at each mint, are all 20 sets of dies used simultaneously so to avoid mixing first strike coins with new dies, with later struck coins from older dies? Thanks!

Thanks Taclough, that helps a little bit I think. Gives me something to think about.