One of them was UK and it was sent to an old address in UK but I had it forwarded to my Caribbean island by old landlord. I was a resident non-dom so just misunderstanding but the bureaucrats still require you to fill en empty tax return as time window for claiming verbally you were non-residence to HMRC hotline (and hence no need to complete tax return) had expired. The letter seemed cookie cutter and not personal but had enough info for me to work out source of info. It had been forwarded before already - having been sent to country X where I held the bank account. It could easily have been lost in the mail and I would have been none the wiser about it all. However I cannot 100% prove it is CRS or HMRC had a crystal ball but I can think which is more likely.
Would be good to know if anyone has had experience. I heard some tax offices just send out audit letters and wait for you to lie.