Meaning difference and tense harmony

Question

This is going to be a two-part question.

1.It's been a long time since I've seen him.

It's been a long time since I last saw him. (or ..since the last time I saw him)

Do the above sentences mean the same thing?

2. It'd been a long time since I last saw him.

   It'd been a long time since I'd last seen him.

Do both the sentences, again, mean the same thing?

When we're using the past perfect, do we keep the entire thing in harmony, or could move the next tense to the simple past? Like, "I hadn't seen him since we were in school together.", or should it "I hadn't seen him since we'd been in school."

Answer 1

There is variation in the way native speakers use tenses, but the present perfect and simple past in your sentences would have different meanings for me.

It's been a long time since I saw him.

I saw him on a particular occasion and that was long ago.

It's been a long time since I've seen him.

I saw him on a number of occasions in the past, perhaps even fairly regularly, and the most recent of them is quite a long time ago.

It had been a long time since I'd last seen him.

This sentence is referring to a time in the past, at which time it had been a long time since you had set eyes on him, and you had done so on a number of occasions. last makes explicit the meaning implicit in the tense that there had been multiple sightings.

It had been a long time since I saw him.

This sentence is referring to a time in the past, at which time it had been a long time since you set eyes on him on that one occasion.