develop的用法老师告诉我们!! develop 作形容词时,developing表发展中,而developed表发

develop的用法
老师告诉我们!! develop 作形容词时,developing表发展中,而developed表发达,比如 CHINA is a developing country,but the US is a developed country .
而 我看见几句话是这样滴
her hometown become more developed .IN the past china wasn't well developed. 这两句话中的developed 都不是发达的意思,那为什么不用developing 呢? 再问一下, well 是不是修饰developed的固定词哇?!