When are we not ourselves?

[Angrboda]

By your method the baby being born isn't even the same person as when the first cell division happened so how can you ever be the same as you were before.

You aren't.

Look at a river. Close your eyes for a few seconds and open them back up. Are you looking at the same river? The water has all been replaced. What you first looked at is now gone.

We are the same as the river. We have the same name but the water has changed.

You seem to be arguing that 'I' am nothing more than my cells. I find this a false notion. 'I' am a model of things associated with my brain and body maintained by the mind. As a process, changes of state are to be expected, but I am not any one particular state. Just as a 'river' is an abstraction for a body of flowing water, the 'I' is an abstraction describing a person. The individual molecules making up that person are not the abstraction.