have .since did区别have .since have done?

问题描述:

have .since did区别have .since have done?
eg:
I haven’t seen you since I’ve been back.
I haven’t seen you since I was back.

since解释为自.以来时,后面应接一个时间点,而不是表示过程的完成时哦,第一句是不是写错了?