> Aditionally, those releases do not only contain FreeBSD changes but also changes to all third party open source packages that are part of the distribution No

> Aditionally, those releases do not only contain FreeBSD changes but also changes to all third party open source packages that are part of the distribution No they don't. Only major releases so, which are once every 2 years or so. And the old ones stay supported until the release after that. There's always two major releases in support. So you have about 4 years.