Top U.S. executives have received billions more in compensation than previously reported, a Reuters analysis shows. Though company filings originally had a group of around 300 CEOs pulling in a combined $16 billion between 2009 and 2013, bull markets have pushed that total to $22 billion.

Every year, publicly traded companies are required to report how much their executives receive in base pay, bonuses and company shares. These filings generally calculate stock options at then-current stock prices. But as share values rise, the overall compensation from previous years balloons. The calculations do not include pensions and perks such as corporate jets. 

As a result, CEOs have earned far more than initially reported -- about 38 percent more, according to Reuters. Over the same period, median wages for American workers increased just 6.7 percent. The 331-fold difference in income between CEOs and the average worker in 2013, as reported by the AFL-CIO, likely underestimates the real gap.

The discrepancy between the executive pay that companies disclose and how much CEOs actually end up taking home highlights the increasingly important role of stock-based pay in executive portfolios. Even when CEOs underwhelm in their performance, galloping markets can boost their overall compensation.

The highest-paid CEO, John Martin of the biotechnology firm Gilead Sciences, netted $400 million between 2009 and 2013, far more than the $75 million the company had originally estimated. Gilead's soaring share prices account for the difference.

Some company leaders weren’t lifted by the rising tide, however. Jeff Immelt of General Electric and Larry Ellison of Oracle both made less than originally reported, due to stock price underperformance and slow profit growth, respectively.

On one hand, the $6 billion discrepancy in executive pay reflects good news: The stock market roared ahead in the years after the crisis, benefiting not just titans of industry but public-sector workers invested in pension funds and anyone with a 401(k).

Less than half of Americans, however, actually own stock, either directly or indirectly. The market exuberance that has inflated CEO pay beyond corporate expectations in the past five years hasn’t yet touched millions of ordinary Americans.