We have the option of creating new downloads for each new link, but that also resets the analytics for each download. It just usually makes more sense to keep the same download but change the link. I'm not sure why itch.io doesn't update the date when the download is updated.
I was unaware of that. It still makes no sense as to why there is no "Last update: " line for the last time you updated the files in the download. Maybe this is something that we could potentially petition to have implemented? It would be nice to be able to see the date of the latest update in the "more information" button.