correct tense ?

1a. While sitting in the sun, the old man fell asleep.
1b. While sitting in the sun, the old man had fallen asleep.
2a. He made several beautiful kites.
2b. He had made several beautiful kites.
3a. We anticipated this happening.
3b. We had anticipated this happening.
4a. You would have been successful if you listened to my advice.
4b. You would have been successful if you had listened to my advice.
Please correct the above sentences with correct tenses.
Thanks.

  1. A
  2. ‘Has made’
  3. Either is good, for there’s no specified time.
  4. B
  1. both possible in different scenarios.
  2. both possible in different scenarios.
  3. both possible in different scenarios.

When and how can you choose b in #1 and a in #4?
Thank you.

No, choice of ‘a’ in 4 is not strictly grammatical. Educated users avoid it, especially in formal written language.

I should not dismiss it so readily without a context.

You cannot normally use 2b and 3b unless they are related to some other happenings in the past as in:
He had made several beautiful kites when he left school.
We had anticipated this happening before we heard the news. (‘We anticipated this happening before we heard the news’ is also possible and acceptable.)

Usually, one of the common uses of the past perfect is to indicate the past in the past; that is, when two activities take place in the past, the first/earlier one is put in the past perfect.