Alex read a book while Amy watched TV.

[5jj]

"Have you already written the book today?" "Yes, I have" (It's 20% finished now)
"Have you ever drawn a picture?" "Yes, I have" (I stopped drawing the picture at half way)

You are still trying to put to much meaning in the tense/aspect.

I think this thread will become too complicated if we bring in present perfect forms. Please start a new thread with this question. Let's just stick here to past-tense forms.

 

[Tarheel]

Thanks a lot! It really helps!

I didn't know we can use verbs in an 'atelic' sense.

"Have you already written the book today?"

That's very unnatural. "Have you finished writing the book?" would make sense (if that's what you want to say).