When the links were posted is irrelevant. They are just directing your computer to a file on a server. That file can be updated whenever. When you go back and click the links in the old posts they will still take you to the new file. People noticed the change at about 8 am this morning.
Once I was able to see how the OP was able to access the slides I put my suspicions to rest. I was skeptical at first but this look legit to me.