If you have an iphone on an old version of ios, you can install the latest version of some software you bought/downloaded for free compatible with that ios version.

Or you get an error and can't do that despite the popup prompting you to do so

Steam often provides every version of a product. (The ui has no option to download them, but you can fetch them via the builtin console)

This is irrelevant since your steam game license applies to all subsequent versions. The argument is it's immoral sell version specific licenses with no way to get to said specific version.

This is a little tangent, but up until somewhat recently Apple hosted ftp servers with old versions of Mac OS available. So you could get system 7.6 (released 1997) straight from them for a new install on your old machine. I think that is no longer the case, but within the last decade you still could. (I think, idk, time flies)

Amusingly, download.info.apple.com still appears to serve all the files that used to be on the old FTP site, including a small and somewhat random subset of old system software versions for Mac and Apple II, Newton firmware updates, etc., but directory browsing isn't enabled, so you need direct links, which you can get from the Wayback machine[1].

But once you have the links, you can download the actual files directly from Apple, e.g., if you're ready to upgrade your Mac Plus to the latest and greatest version of System 6, download

https://download.info.apple.com/Apple_Support_Area/Apple_Sof...

https://download.info.apple.com/Apple_Support_Area/Apple_Sof...

https://download.info.apple.com/Apple_Support_Area/Apple_Sof...

https://download.info.apple.com/Apple_Support_Area/Apple_Sof...

[1] https://web.archive.org/web/20141025043714/http://www.info.a...

That's because they allow you to download new updates with your existing license.

In this case, the existing license is only valid up to a certain point, after which you need to buy a subscription (because the perpetual license wasn't quite so perpetual).