Check out the references below, we see that Japanese has the same problem as Chinese: Does "以X" include the word itself, eg. is 1 included in "1以上"?
As what I have seen, in old Chinese books, there are "以" and "已" expressing the same(?) as in 以上/已上 以下/已下. Even 史記 itself used both (according to its "tables", confusingly, the Chinese Wikipedia page used "以" instead).
Answers come from the references simply gave us the answer and didn't say why, that's the reason why I come here for an authoritative answer.