Apple Not 'Fully Patching' all OS's

Implications?  And to what degree?  Only most serious, and how often?  So what then is an upgrade? seems perilous for users.   Also in Schneier with comments, 

Apple clarifies security update policy: Only the latest OSes are fully patched  in ArsTechnica

New document confirms what security researchers have observed for a few years.

ANDREW CUNNINGHAM - 10/27/2022, 12:18 PM

Earlier this week, Apple released a document clarifying its terminology and policies around software upgrades and updates. Most of the information in the document isn't new, but the company did provide one clarification about its update policy that it hadn't made explicit before: Despite providing security updates for multiple versions of macOS and iOS at any given time, Apple says that only devices running the most recent major operating system versions should expect to be fully protected.

FURTHER READING

PSA: Apple isn’t actually patching all the security holes in older versions of macOS

Throughout the document, Apple uses "upgrade" to refer to major OS releases that can add big new features and user interface changes and "update" to refer to smaller but more frequently released patches that mostly fix bugs and address security problems (though these can occasionally enable minor feature additions or improvements as well). So updating from iOS 15 to iOS 16 or macOS 12 to macOS 13 is an upgrade. Updating from iOS 16.0 to 16.1 or macOS 12.5 to 12.6 or 12.6.1 is an update.

"Because of dependency on architecture and system changes to any current version of macOS (for example, macOS 13)," the document reads, "not all known security issues are addressed in previous versions (for example, macOS 12)."

In other words, while Apple will provide security-related updates for older versions of its operating systems, only the most recent upgrades will receive updates for every security problem Apple knows about. Apple currently provides security updates to macOS 11 Big Sur and macOS 12 Monterey alongside the newly released macOS Ventura, and in the past, it has released security updates for older iOS versions for devices that can't install the latest upgrades.  ... '