What you are describing happens all the time. Usually the toolchain provider will continue updating a list of known issues for some time after EOL. Beyond that you have third parties that do it for decades, if the platform is big enough. They collect bug reports from the industry, investigate them, then create lists that you subscribe to. Those lists include detailed examples, explanations, and usually linter rules to detect code that could trigger the bug.

The truth is: If the toolchain was good enough to ship your product, has time to go EOL, and then you do a patch that surfaces an esoteric toolchain bug, then the odds are that you'll know exactly what triggered the bug and you can work around it by writing different code.

Because even if the newer shinier compiler/toolchain had the issue fixed, most companies wouldn't upgrade to it at that point. It's almost never desirable to change your toolchain for a shipping product, you're just introducing more unknowns.