Actually, can you explain that more? Since yahoo adjusted close says it takes dividends into account, I took that to be the same as immediately reinvesting your dividends in the same holding. You're saying that instead, it's the same as issuing the dividends as cash and then forgetting about it?

If so, then how do people actually backtest long term holdings to assume reinvested dividends? As far as free historical data sources, I thought it was basically yahoo or nothing.