Follow your clue, I would further speculate:
In July they moved completion date from 28 to 24th, it is because someone who was supposed to finish 52 week by 28th met the endpoint of loss of control and left the trial. This patient was the very last randomized recruitment in late September 2017. He/she could be a placebo or AZD1419. He might have a couple of months (upto 6 months) asthma control.
More important, this also means someone who supposed to finish on 24th are still going strong without loss of control, at least in July. That is half a year after last dose of AZD1419.
The closer we get to Sep 24th, the longer lasting AZD1419 works, and the larger potion of patients don't even meet the endpoints at all.