What version of macOS are you on right now? Those links will only work on Macs that can support the OS you want to download. So if you are already on Catalina, for example, none of the links will work since I can't go back.
On my 2009 iMac, running High Sierra, it will not show the El Cap, Mojave or Catalina installers since I can't install it on that machine. If my experience with my MBP, running Catalina, is anything to depend on, then I won't be able to see the older version of macOS either on my iMac since I can't go back to an older version.
At the end of the day, the ONLY way to reliably have a version of a installer is to grab it when it becomes available on the App Store and save it somewhere. Otherwise, it's getting harder and harder to grab the installers legally.