Robert1893:You're probably saturated at your tier. I think for Tour Master it's the top 50 scores.
The latter is correct but I'm not sure about saturation. If you are saturated you must have a tight bunch of scores. A saturated average of 69.82 would include 3,491 strokes, 69.74 makes 3,487 strokes. So your 66 replaced a 70 which would have to be the highest score included in your average.
I'd find it really surprising, although I know it's possible, that an average (based on 50 rounds) of 69.82 didn't include a score higher than 70.
My guess would be you're not saturated but are close; say 45 rounds, 69.82 x 45= 3,141.9 strokes add 66 = 3,207.9 and divide by 46 would give an average of 69.737.
Hopefully you're not saturated as that will mean your average will come down faster when you are.