That's not true and the v8 team's stance is pretty clear. The master branch is the only "fully supported" code base, currently at 4.2.56 [0]. Most other tagged versions going back a year or two receive best effort support. Usually, that means Ben Noordhuis, but often Andreas, Yang, Vyacheslav, and others on the v8-users and & v8-dev lists. Good responses all around in general. And the list of responsive people continues to grow.

[0] https://github.com/v8/v8-git-mirror/tree/4.2.56