Registering WinRAR in 2021: How Far Back Does It Work?

"Nobody registers WinRAR." So let's register WinRAR! It's notorious for its infinite 40-day trial so I've been curious what activating it is actually like. I also wonder how old of a version of WinRAR can be activated using a 2021 registration key! Let's find out with Windows XP, 98, 95...