Trying to install an old OS, but no disks show up

Everything has worked fine disc-wise up until now. I’m trying to download an older OS in a separate disc via CMD+OPT+SHIFT+R but in the OSX downloader I can only get so far as the disc selector because none show up. I did the same procedure just over a month ago. I split the disc, didn’t work. Then tried to follow some troubleshooting from other people’s questions, but I don’t know the lingo too well. But I don’t think any of those applied anyways because they were trying to download newer OSs.