I have thought about that as well, but then couldn't you say the exact same thing about growing up? I mean I am in some ways vastly different from the 5-year old me, but still I share my past me's memories, and memories of becoming present me. In that sens I guess you can view a person as a symbol, "I" encompassing all "me", past, future and present. But I agree it is problematic especially if you take into account possible mental enhancements/engineering.