Ditto. But going the opposite direction, you are cautioned to use Excel''s menu of file-types when saving a file under current versions, hoping to use the files under the old version.
It is hard and expensive to keep up with progress. Personally, I think Office 2003 had achieved a level of sophistication and features that match my needs, but you eventually find out when support has ended. I'm still using Office Pro 2010 on a couple machines, and I just bought legitimate licenses for the 2013 version. Without telling the story about how I recently acquired my first new laptop, I can say that I uninstalled the trial Office 365 from it, and installed the 2013 license. My disdain for the subscription software model continues.