I think you added an extra three zeros during your total year calculations. you list 2.23E15 as the total number of years experienced, but multiplying the total time of 5E4 by the current population of 8E9 gives a total of only 4E14 experience years. The true number must be quite a bit lower as the human population was quite a bit lower than 8 billion for most of that time. This also affects the proportion of experience years which have occurred in living memory. My guess is 20% have occurred since the birth of Kane Tanaka and 10% experienced by living people. This also squares pretty well with your figure of 50% of human experience occurring since 1300. It doesn't really make since for 50% of experience to have occurred since 1300, but only 0.02% since 1903.