I firmly believe that if they were measuring today exactly what they were measuring 12 years ago, you would see a decline.
I am not so sure. The 15 minute rule was introduced, what, like nearly a decade ago. Just how long exactly can it go on being blamed for increases? Logically it would have resulted in a one time increase. not recurring year on year gains indefinitely. And how many inactive parents are there having studies with their children anyway? I am not sure I understand this point.
My own congregation seems to be on a slow decline, and that despite a few recent converts.
It would be good to have some independent check on the number of Witnesses in the UK, but unfortunately the census question on religion in the UK was pretty useless.