This article, at least, talks about income, rather than wealth. Income we have a concrete measure for, at least, rather than attempts at estimation with giant unknown error bars. But income isn't a stable metric either. The IRS has been continually changing rules over time. Most notably, there has been a consistent push to crack down on "fringe benefits" and make them taxable. "Company cars" and things like that are essentially dead.

To some degree the changes in the income characteristics here reflect changes in the nature of compensation, from various tax dodges to just cash compensation. It was once easier to give executives a car for their exclusive use, rather than pay them the value of the car, since it was an allowable business expense. That is no longer the case (unless the car is intrinsic to their job) so rather than giving them a car and paying taxes on it, they just give them the money and let them buy their own car.

To what degree does this inform the changing characteristics of income in the top percentiles? That's an unknown question, but the best answer we have is just to assume that nothing has changed in the actual income distribution except the switchover from fringe benefit based compensation to taxable compensation. But that, unfortunately, renders moot the entire point of articles like this, about "worsening disparity", which is a convenient bogeyman to point to about the dangers of unchecked capitalism. So instead, we just pretend that this doesn't exist, and we continue to use made-up numbers to try to make a social point.