UPDATED: From where is the AP getting $1.5 trillion?

Yesterday's article which announced that the cost of the Democratic-backed health care reform was $1.5 trillion caused big waves since a) the CBO hasn't officially announced how much it thinks the plan will cost (and its preliminary tab was $1 trillion) and b) the AP's only source was an anonymous Hill staffer, which seems rather thin for such a controversial claim.

As CF noted:

Where is the extra $500 billion coming from on top of the CBO score? What provisions did the CBO not score? Why does this anonymous aide think those provisions cost half a trillion dollars? Does anyone else agree with him or her? Readers wouldn't know from the AP article.

The AP has a new piece up that at least tries to detail where the costs come from. But didn't the AP get the chronology wrong? Meaning, shouldn't the details have been offered up first?