The former deputy attorney general, Jamie Gorelick, the only member of the 9/11 commission to read the president's daily brief, revealed in the hearings that the documents "would set your hair on fire" and that the intelligence warnings of al-Qaida attacks "plateaued at a spike level for months" before September 11. Bush is fighting public release of these PDBs, which would show whether he had marked them up and demanded action.

Pincus in the Washington Post, 2/12/04:
Miscik also said there would be a review of the President's Daily Briefing, the bound book presented each morning to Bush with the most sensitive, latest overnight intelligence. Saying the PDB had been "dramatically revamped" in a way that "significantly improved the quality of the product" when Bush entered the White House, she said there would be a comparison with the material presented to President Bill Clinton "to see if some of the strong points of our earlier approach have been lost."

According to a senior intelligence official, the Bush version added "more sensitive operational information" and dropped some of the accompanying graphics that helped in understanding the substance of the material. In addition, the Bush PDB gets a more limited distribution within the agency, leaving some senior analysts unaware of what has been sent to the White House.

And from 2/11/04, 9/11 Panel to Accept Summary of Briefings
Legal Challenge Scrapped;
Agreement Angers Some Members, Victims' Families

Dan Eggen, Washington Post Staff Writer:
The independent commission investigating the Sept. 11, 2001, attacks backed away yesterday from a threatened legal showdown with the White House, agreeing to accept a 17-page summary of the presidential briefing documents it had sought.

The deal will not allow the full 10-member commission to read the original documents or to have access to notes on the documents taken by some of the commission's own members. The summary -- provided to commission members during a closed-door meeting yesterday -- covered several dozen original intelligence documents and was first vetted by the White House, officials said.
[...]
Under the original November agreement with the White House, four commission representatives -- Zelikow, Kean, Vice Chairman Lee H. Hamilton (D) and member Jamie S. Gorelick (D) -- had access to two dozen PDBs that the White House had preapproved as being relevant to the commission's mandate. In addition, Zelikow and Gorelick were able to comb through several hundred other PDBs from the Clinton and Bush administrations in search of information they deemed relevant.

From notes taken during these reviews, Gorelick compiled the 17-page summary provided to the commission yesterday, which was approved by the White House, officials said. Gorelick, a deputy attorney general in the Clinton administration, said the summary provides the commission with "the most important and salient facts" from the documents.

A-ha!  I think what we're getting released is a summary and not all the intelligence in that day's PDB.
5/17/02, Dan Eggen and Dana Priest in the Washington Post:

The Aug. 6 briefing, according to officials with first-hand knowledge, was different. Along with current intelligence, it had a 1 1/2-page analysis -- largely speculative -- of what bin Laden might have been planning. The summary analysis was requested by Bush, according to White House spokesman Ari Fleischer.