When there's new information on a story, do we delete or amend?

Yesterday an Amber alert was issued when a truck in Grande Prairie was stolen with a seven-month-old baby still inside. Since I have a number of friends/followers in communities near Grande Prairie, I posted a photo of the truck along with a description and licence plate number issued by RCMP to help spread the word.
Within hours, RCMP announced they had recovered the child and the alert was rescinded. I deleted my previous posts, and wrote a new one saying “Amber alert is over, 7-month-old found. Since it is over, I have deleted previous posts, but thank you for sharing.”
I rarely delete posts (unless it’s an immediate correction of a spelling mistake I didn’t notice while posting), preferring to correct and update later while letting the record stand. The reason I deleted in this case is I did not want the Amber alert to continue to spread once it was over.
In a story about the potential drawbacks of Amber it is noted that police carefully consider when to issue an alert because they don’t want the public to become desensitized to them being issued. When one goes out, they want it to mean people should be on notice. My feeling is that if an inactive alert continues to spread through social media, it contributes to a general desensitization: if you keep seeing alerts that are no longer alerts, you’ll pay less attention when an active one comes up. So I delete in order to stop the spread– my hope is you’ll only ever be able to see an amber alert on my Facebook and Twitter pages when there is one active- the old ones are gone.
However, I received a good counter-argument to this notion from Tyler Neilson, another active social media guy and smart thinker. His argument (edited from a Facebook conversation) is as follows:

“I always wonder if the original post should just be updated to give the rest of the story, rather than deleted…. I look at my feed and there are still 10+ links to articles which warn of the Amber Alert, at least 1 of them coming in after the amber alert had been canceled…

“Your follow-up is the only one in my feed, and there are now 15 posts/shares about the amber alert that I can see …

“This post [about the alert being over] has not been shared, and your other post that had been shared could have been rewritten to instantly get the correct information out (and at a higher likelihood of being seen based on the existing interactions) … you already had the broadcast in place, and you could have updated the message. Now as people look back through their News Feed for your informative post about a breaking news situation they may or may not see this, they certainly won’t see the other, and they are likely to come across many other posts which have not been updated (nor deleted). My thought was that you had a chance to provide some balance …”

His point is that if I had updated, rather than deleted, the original post all the people who had shared it would have now been sharing the new information. By deleting, all I’m doing is taking away the old information- but since other people have posted the same old information it drowns out the new information. Plus my new information about an alert being over isn’t likely to be shared as much as the old information about the alert being issued.
I see the point, and I think I would use it in most cases, but I think I’ll continue to delete in cases such as this one. Happy to hear other thoughts, though!