In my previous post, I had explained that Yahoo and Google EOD (End of Day) historical data does not match.
Let us take a look at XOM. On 12/30/1994, Google reports the close price as $43.85. Yahoo reports the close price of $87.35 and also reports an adjusted close of $35.53. Y! adjusted close prices are adjusted for any splits and dividends. On the other hand, Google only adjusts for splits.