If you access a Yahoo! file by a direct link:
then the link will always work.
However, you have to access that direct link by yourself, since it is not the link that Yahoo! normally presents to you. If you take a close look at the bottom left of your browser window when you're hovering over a Yahoo! file link, or just right click on the link and hit "copy link location" and paste it somewhere to take a look at it, you will notice your Yahoo! link actually looks something like this:
The "garbage" part of that URL filled with seemingly random ASCII characters changes every 2-3 minutes or so, presumably to make sure you're downloading the file from the latest version of the group page. (In fact, that URL has already changed twice since I started writing this message.)
End result: if you load the page and take a while to look for the file you want, the URL might have changed meanwhile and you'll be stuck with a page full of dead links. If you want to guarantee access to a file (e.g. sending the link to someone) make sure to use the "direct link" format posted above.
Edited by James, 25 August 2013 - 06:33 PM.