It still depends to an extent on which processing center and then who's desk/s it lands on. Behind them telling you when you call them for progress updates and they tell you "We can only see what you can also see on your computer monitor screen at home"--there is a human element and an overall labor force element--the number of cases per employee involved.
Of course if the petitioner is fast and accurate in submitting paperwork, that always helps too. (until it ends up on the bottom of a pile on some lazy worker's desk)
I was wondering which USCIS processing center's currently fastest and if this couple, by luck of the petitioner's USA location, got that site. When we filed, it was in the state of Vermont and I think Nebraska was next. We started out in Texas, which was overloaded so bad that they moved our case to California, which added delay.
Sometimes the Embassy in her country gets backed up too--physicals and the crucial interview can create delays. In short, there's a number of elements and it sounds like this couple were efficient, as well as lucky.
We didn't even try contacting our Congressman or Senator--in the past, they've helped us get new passports quickly and cut red tape in other areas, but when we were filing our K1, there wasn't much even they could do. The USCIS was really a force unto their own.
