Take GM. In 2008, GM trailed Toyota by about 1.2 million units. Toyota's sales fell 4.2 percent from 2007 to 8,972,000, while GM's fell 12.3 percent to 7,790,245.
But by the end of 2009, GM will have lost the Saturn, Hummer, Pontiac and Saab brands. Global sales of those brands totaled 720,550 in 2008. It remains to be seen how many of those customers will migrate to other GM brands.
More important, GM's tally may no longer include sales of Opel and Vauxhall. How those brands are counted will depend on the outcome of GM's efforts to sell part of its European operations. If GM no longer owns a majority of Opel/ -Vauxhall, those brands' sales would not count toward the GM total.
That loss could shake up the rankings. In 2008, Opel and Vauxhall's combined global sales totaled 1,503,100. Take away from GM the global sales of all those brands — Opel, Vauxhall, Saturn, Hummer, Pontiac and Saab — and the Detroit automaker would have fallen to No. 4 in 2008, behind Volkswagen AG and Ford Motor Co.
If bidder Magna International Inc. succeeds in buying control of Opel, it aims to make vehicles for other companies using Opel architectures. So the Opel sale could be not just a loss for GM's sales total but a gain for some rival or rivals.
Fiat S.p.A.'s initial stake of just 20 percent of Chrysler means that the two companies' sales totals will continue to be counted separately, as are Renault SA and Nissan Motor Co.'s sales. But that could change if Fiat eventually obtains majority ownership of Chrysler.
If the two automakers' sales had been combined in 2008, the Fiat-Chrysler total would have ranked fifth in sales.
For that matter, Renault and Nissan combined had sales of approximately 6.1 million in 2008. If they were a single company rather than a partnership of two automakers, that would have put Nissan-Renault at No. 4.