Use of present perfect in specific context

Hi. Please help me with these three situations involving what I think is the choice between the use of present perfect and past tenses.

1. I think we can use the present perfect tenses when a person writing for John Doe is writing sort of a recommendation (as noted) shortly after his having lived, attended, or worked in or at the place(s) noted. Let us assume the letters "XXX" represent a certain place he lived in, attended or worked at. What do you think?

Hypothetical situation: writing sort/kind of a recommendation

John Doe has lived in XXX/attended XXX/worked at XXX for the past three years and founded him to be ...

2. I think we could either use the past or present perfect tense in this situation and both are correct. But since it was spoken right after the birthday party, I happen to think the use of present perfect might be better. (I am not sure I wrote it clearly to reflect what I wanted to say, though.)

Hypothetical situation: talking to a host right after a birthday party he enjoyed

I enjoyed/have enjoyed the party. It was a great party. I hope I could have a party like that for my birthday. Great to be here. Talk to you later.

3. Again, I think we could use either the past or present perfect tense and both are correct, although the present perfect tense seems better. (I am not sure one is (in fact) better than the other, though.)

Hypothetical situation: a teacher talking after looking at a student's homework assignment for a short time

I see you completed/have completed all your homework. I will look at it more closely and assign a grade for your homework.