It is a psychological effect, 'asked and answered'. That is why nursing homes always do better on the second and third survey on QIS. The resident has already 'been asked' and has already 'answered' these questions before. So when they are asked ' have you ever?' in their mind this question has been 'asked and answered' and therefore does not give a negative response.
So you are correct most nursing homes only need to ask the questions time and time again, and the negitive responses will go away for the most part. And since over 60% of Stage 1 issues that can trigger a Stage 2 investigation are from resident and family interviews, just ask and ask away.