They haven’t received any junk mail since they/"they've" moved house.

[sitifan]

Since and tenses​

When since introduces an action or event at a point of time in the past, we can use the past simple or present perfect after since and the present perfect in the main clause:

1. They haven’t received any junk mail since they moved house.

2. They haven’t received any junk mail since they’ve moved house.

We can use the past simple, present perfect or past perfect after since with the expression it + be + time + since:

3. It’s been years since I rode a bike. (it’s = it has)

4. It’s been years since I’ve ridden a bike. (it’s = it has)

5. It’s years since I rode a bike. (it’s = it is)

6. It’s years since I’ve ridden a bike. (it’s = it is)

It’d been years since I’d ridden a bike. (it’d = it had)

It’s been years since … is more common in American English than It’s years since ….
When since introduces a state in the past that is still continuing in the present, we use a present perfect form of the verb after since and a present perfect form of the verb in the main clause:

Since I’ve been back at work, I’ve been feeling great.

(My bold.)
Source: https://dictionary.cambridge.org/us/grammar/british-grammar/since

Are #2, #4, and #6 really acceptable to native speakers of English?

 

[dunchee]

Yes.

 

[jutfrank]

4 and 6 are perfectly natural, yes. I think 2 is debatable.

 

[sitifan]

3. It’s been years since I rode a bike. (it’s = it has)
4. It’s been years since I’ve ridden a bike. (it’s = it has)
What's the difference in meaning between #3 and #4?

 

[emsr2d2]

3. It’s been years since I rode a bike. (it’s = it has)
4. It’s been years since I’ve ridden a bike. (it’s = it has)
What's the difference in meaning between #3 and #4?

None. In both, the meaning is "The last time I rode a bike was years ago".

 

[Tarheel]

Is "move house" British English?

 

[5jj]

Yes. We often omit 'house' when context makes the meaning clear.

 

[Tarheel]

We have moved several times. It's the same thing, but I have never moved house, and I would be surprised to hear that. I can't be 100% certain, but I think it's another American English/British English difference.