John Foley,
An 11 point change seems high to me also. Did the course rating change? If the course rating went down, it is possible that the bogey rating didn't change and that would account for the difference. Courses get re-rated every 5 to 7 years (new ones get a second rating 1-3 years after they open.)
Where you playing it 5 to 7 years ago? If so, can you think of other changes such as rough height or green speed that might make a difference.
Most of the time that we re-do a rating a change of 3 or more points would seem like a lot without some set of changes.
The rating is not calculated on the scores that people are shooting, it is based on a set of measurements and tables in the course rating guide.
If the slope went up that much and the course rating didn't change, lots of peoples handicaps are going to come down in a hurry.