Yesterday morning the Boston Globe committed an error of journalistic etiquette. Its instantly famous story on the timing of Mitt Romney’s departure from Bain Capital failed to credit two outlets — Talking Points Memo and Mother Jones — that had done significant reporting recently on the same topic. The paper took the somewhat unusual step — at least for a big newspaper — of reopening the Web version of the story and inserting the appropriate references.

A statement from the Globe juggled graciousness and assertiveness:

Pieces of this story were reported by other news organizations. We believe the Globe advanced the story with a more comprehensive and complete look that broke significant news and included additional documents. However, our policy is to give credit to other news organizations for their work. In the editing and shortening process, I have learned, passages giving credit were removed. That was a mistake, and we are now adding appropriate credit back to the online version.

The Globe’s corrective generosity raised a classic media question. Hey, why didn’t this story blow up earlier this week, when TPM hopped on it, or last week, when Mother Jones did? Some guesses:

1) Standing. The Boston Globe is a member of the mainstream media, whose stories always get preferential treatment before the Internet’s Board of Viral Promotion (BVP). “It’s a big metro daily,” says Josh Marshall, publisher and editor of TPM.

2) Content. Globe Editor Martin Baron expresses reluctance to engage in guesswork as to why the Globe piece drew so much more attention. When pushed and pushed and pushed, though, he coughs up a few words in support of the story’s substance: “We pulled it together in a cohesive and comprehensive way,” says Baron, who notes that the story pulled in a hefty haul of Securities and Exchange Commission documents on Romney’s role with Bain Capital during the disputed period (1999-2002) and testimony from a residential dispute in Massachusetts when Romney was running for governor of the state.

3) Expertise: TPM and Mother Jones can write about Romney till their WiFi breaks down, but few outlets can command the attention of the Boston Globe when it comes to the background of Mitt Romney. Its reporters Michael Kranish and Scott Helman cranked out the book “The Real Romney,” which the paper calls the “first complete, independent biography of Mitt Romney, a man whose journey to national political fame is at once remarkable and thoroughly unsurprising.” When the sponsor of “The Real Romney” speaks up, people link. “The Globe people are considered the gold standard for Romney’s past,” says David Corn, the Mother Jones journo who wrote last week’s story on the matter.

4) Hot Griddle. The story landed just as the Obama and Romney campaigns were bashing each other over the question of outsourcing, a wrestling match tied to Romney’s record and tenure at Bain Capital. Says Corn: The Globe “had the advantage on a day when the two campaigns were locked in this particular debate due to political ads that have come out. It’s often ads that drive the narratives that drive campaign coverage.”

Citing a brand-new Romney ad hammering the Obama campaign’s depiction of the Republican candidate as a champion of outsourcing while at Bain, Marshall noted: “This was supposed to be their big pushback day . . . and to have their own [hometown] newspaper say this . . .

5) The Great Unknown. Even people who’ve spent ungodly amounts of time embedded in news cycles are left guessing as to exactly why one story changes the world and another doesn’t. “You know, I’m not exactly sure,” says Marshall when asked about the disparity.