Never. And that is definitely not a complaint. Kudos to PG Music for fixing them as the arrive. Not every software company is so dilligent.
That depends a lot on how one interprets "stop patching".
Looking theough the history up patches and updates, there is only one most-recent patch of a release since 2007 that is in the subsequent year, and that's 2019's build 644, which was released in January 2020.
That implies to me that they stop bug-fixing each release roughly when the new version is released. If one doesn't "upgrade", the bug-fixes stop, but if one does "upgrade" one gets a bunch of additional new bugs.
As far as I'm concerned that means they stop patching bugs at each new release. I think one reason for that is that at each new release it's
"all hands to the pumps" to deal with the new bug reports from users of the new release.