I think the important thing is that if the host computer is Debian "Bookworm" x86_64, it's not possible to progress from 3.0 to 3.2. This build did work on older systems.
It works a bit different: the bootstrap compiler is
always the previous
release version, and
the only documented bootstrap compiler, but there is sometimes a grace period allowed
if, and only if, compiler changes would still allow a bootstrap with an older version. In such cases the grace period is removed somewhat later.
As such this can greatly vary between updates. After a previous version is updated in such a way that the new compiler relies on new features introduced in the bootstrap version, this is not possible.
Hence sometimes an older version can be used as a bootstrap compiler, and sometimes not and this can vary per release. So the statement that it "worked in the past" is false: that is and has always been dependent per release.
Note that the other way around is also possible. There is a make parameter called OVERRIDEVERSIONCHECK=1. You might assume that you can then build with another version, both older or the same as the newests release. Alas, the same as above: it is possible that the newest version relies on features from the previous stable release, so you can not bootstrap the latest release with itself because some features may have disappeared or changed in implementation (the breaking changes)
Unless you pretend to know what you are doing only the adagium "the bootstrap compiler is
always the previous
release version" holds.
BTW: the build scripts always can tell which version(s) are allowed for your particular bootstrap.
So, I hope it is clear it has nothing to do with "previous versions"
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