Included or Not Included As In "以後" "以來", etc
In ancient Chinese, 以上 and 以下 are inclusive without a doubt. Why? Just because everyone use them in the same way and exceptions are few to none. Example:

三品以下用金宝，二品以上用玉宝。（元史•选举志三）
七月，定进马迁赏格，每甲马一匹或二匹以上，迁赏有差。（金史•列传
第五十七）

In modern Chinese, they are supposed to inherit the ancient usage, however sometimes people try to be accurate by adding explanatory words which actually diluted the original meaning. For example the following forms are quite common in modern Chinese:

目前，浙江省县及县以下考生占全省考生总数的 68%。
设立公司应有三个以上（含）发起人。

In law space, the usage is still clearly defined to be inclusive. Example:

本法所称以上、以下、以内，包括本数。（1997 年 3 月 14 日修订《中华
人民共和国刑法》第九十九条）

This reference has a lot of examples to demonstrate the ancient and modern usages. (The author considered modern new usages wrong.)