Here are the crucial differences in both counts, that have confused everyone....this is all in a must-read post on Publius
It’s the summation of the electoral acts from each polling place, conducted over a 24-hour period following the close of the last poll, without regard to the normal verification procedures. It’s purely informational and has no legal significance.
“Where does it rank on the pecking order?”
It’s more accurate than exit polls and less accurate than the final results. Legally, it’s nowhere — the information is not used in any way during the count.
“How many countings are after it?”
One. The count. The count starts on the Wednesday after the election, and is conducted simultaneously by 300 electoral councils, one per district. By law, the person responsable for each poll table is responsible for delivering the ballots and acts for that table to the district council within 24 hours (although exceptions may be made for really remote places.) The count starts on the Wednesday to ensure that all the material is available.
So when AMLO was complaining about the vote counts thrown around, he had a valid point. Yesterday the real count began, and the Mexican electoral authorities -- which never wavered - finally began explaining clearly what was going on. And now again - Calderon is slightly ahead, confirming early projections but with a tighter margin.