well in Sons of Mars Abraham リンカーン offers death a coin with "20--". the end of the 日付 was blocked out but it was in the 2000's. so it had to take place sometime in the 2000's otherwise there wouldn't have been anybody around to make that coin. also it can't be past 2100 because then it would have been visible in the coin as (21--). (assuming the coin was pretty newly made, which is probable) then it would be anywhere from 2000-2099 when the wars took place.
if the coin was an older coin (otherwise meaning that the coin was produce well before the wars) than it could take place anywhere past 2000 but not before.
i solved this mystery, the answer is 2000, there are no cars in 996 years ago,in land of ooo ,the 年 is 3000+ in the enchiredeon,there are numbers at its back which resembles 8.13.21 also august 13,2021.