They've become good friends since last year.

English as a Second Language English Vocabulary, Grammar and Idioms
1
  1. They’ve become good friends since last year.
  2. They’ve moved to Japan since last year.
    Are the above two sentences acceptable?
2

Hi Sitifan,

Why don’t you give us your choice first, then we’ll correct you if necessary?

3

Someone says:
sentence 1 is correct.
sentence 2 should be:
They moved to Japan last year/ a year ago.
We use the past simple because the action of moving is complete.

Do you agree?

4

Hi Sitifan

Both of your sentences are fine. They both focus more on the fact that something has happened and less on when it happened.

No.
Sentence 2 does not mean that they moved to Japan exactly a year ago; it only tells you that they moved to Japan at some (unspecified) point in time between last year and now. Sentence 2 is just fine with the present perfect.