I would never dream of going 20000 miles or two years, between services, to me that would then be a car that doesn't hasn't been cared for, my mk6 went 6 months between its last 2 services as it had had done nearly 10000.
If i am buying a car like this i want proof that it has been serviced at least every year regardless of milage and not travelled further than 12000 ish in that year. Or i'd walk away unless it was a very good price, these aren't mk1s and 2s where you expect the history to be patchy in places.
But I'm a bit obsessive apparently.