The problem with the Product List on the site (for these purposes) is that it only lists the product and a link to it.
Every product would have to be opened to check a release date for what Stargrove is trying to create. Release date and copyright date are close enough for these purposes I am guessing.
For newer items the PDF download now includes the date of revision as part of the file name which helps for the last 6 to 8 months or so.