However, given his length of residence and given his proficiency, he should have been deleting more.

但是根据他的居住时间和流利程度，他应该再去掉一些。

After the age of 12, the length of residence has almost no effect on your accent.

12岁以后，居住时间对口音几乎没有影响。

Anna, given her length of residence and her proficiency, which was less, should've been deleting much less.

Anna，鉴于她的居住时间和流利程度都相对较差一些，去掉的部分应该更少。