NASCAR Racing: starting grid, nascar race, starting grid

Question
How come there are 43 cars to start a NASCAR race?liaej

Answer
over the years we would have 50 or 60 cars start at darlington or bristol, so in the 60's nascar mandated 42 cars for each race. In thelate 80's Richard petty failed to qualify for a race. so nascar added the 43 starting position for the champions provisional