Canadian Lawyer gathered salary data from 87 Canadian in-house counsel. I looked at each year out of law school and their ranges, meaning the absolute difference between the lowest salary and the highest salary. They averaged $76,000 but they showed no pattern with increasing years of experience. I would have expected ranges to widen as medians (years of experience) rose. Over time, pay spreads, or so I thought, as people differentiate themselves.
I found likewise with the range divided by the median: no pattern except that years with wide ranges were higher than the average of .75. For this metric, it seems plausible that it would stay fairly stable, for the reason that as medians rise, so does the difference between lowest and highest (but see above).