It would have increased/decreased their taxable gain/loss based on non monetary (to the investor) factors, and those who sold Enron the few years prior to their earnings restatements would have the pleasure of filing amended returns, most likely paying additional taxes, since I would assume if earnings increase your cost basis, losses would reduce it.
An example, buy an airline stock at 10, they report a $3 loss, sell it at 8, pay taxes on a $1 gain. Yeah, this is a simplified system.