Comment by gruez

Yes. Until a few years ago after a new major iOS version was released (eg. 26 for this year) the last major version (eg. 18 for this year) stopped getting updates, at least for phones that had access to the newer version. That changed a few years ago so that there was a period of overlap where both got updated.

For instance, look at the release history for iOS 12 and 13:

https://en.wikipedia.org/wiki/IOS_12#Version_history

https://en.wikipedia.org/wiki/IOS_13#Release_history

After 13 was released (September 19, 2019) there were no more updates for iOS 12, at least for the devices that support iOS 13.