mortality from amniotic fluid embolus

GTG no. 56 maternal collapse 2011 says mortality in more recent studies in closer to 20% (it says survival is 80%). Older books have various figures from 50% to over 80%.

The MCQ says:

Maternal mortality occurs in over 80% of reported cases    Correct answer: True

Do you think we should use the older answer like the MCQ here or more recent data like the GTG, I suppose we are guessing at what the exam board choose is the answer when papers say anything from over 80% to 20%!