What I wrote is valid for GPL 2, which was relevant here because that’s what Wordpress uses. GPL 3, however, offers five options, each written to be more generously worded to allow for more flexibility. One of the new options allows for me to say, essentially, “I didn’t modify the source from upstream, here’s a link to their source code download page; go there and download it yourself”. Some people do this already, but this isn’t actually permitted with GPL 2.