Sometimes the wire services will keep the same URL but change the text in the story and even the headline as more facts become available.
I had this happen to me a few years ago on a story I submitted about Fedex misplacing some radioactive rods.
http://news.slashdot.org/story/10/11/26/1948245/FedEx-Misplaces-Radioactive-Rods
By the time the story was posted the rods had been found and the linked story was a non-story with a new headline:
"FedEx Finds Radioactive Shipment That Vanished Between N.D. and Tenn."
Some newspapers like the NY Times will post a correction at the bottom of the story whenever something changes in the story.
Many don't.
The hardest part of climbing the ladder of success is getting through the crowd at the bottom.