PREP 232 完成时的疑惑

guoqi

The Acoma and Hopi are probably the two oldest surviving Pueblo communities, （both dating ）back at least a thousand years.
A.    both dating
B.    both of which have dated
C.    and each has dated
D.    and each one dating          
E.    each one of which date

请问下笔记里说 B和C选项里 date的现在完成时有潜在含义说“以后都不是追溯到1000年以前了” 是什么意思？ 个人觉得用完成时没必要，但是理解不了这个解释的含义 请大家看看