I think this is a very important point. If it didn't block a previous release, it shouldn't block the current release. It doesn't mean it shouldn't get looked at, but it also shouldn't be a blocker. I think the high priority regressions should be ones that are new to 4.3 because they have clearly been either introduced or exposed by this release and need to be dealt with.
It might happen that a bug is triggered more easily in 4.3 than it is in 4.1 or 4.2, but an artificial test case can be constructed that fails on all three releases. See for example PR32004, where comment#16 has a testcase failing on 4.1/4.2 too.
Paolo
