https://git-scm.com/docs/gitworkflows#_maintenance_branch_ma...

>After a feature release, you need to manage your maintenance branches.
>
>First, if you wish to continue to release maintenance fixes for the feature release made before the recent one, then you must create another branch to track commits for that previous release.
>
>To do this, the current maintenance branch is copied to another branch named with the previous release version number (e.g. maint-X.Y.(Z-1) where X.Y.Z is the current release).

Чётко: хотите сопровождать старые релизы: создавайте соответствующие ветки.

Почему же сами разработчики git используют какую-то другую технику, и где она описана?

Documentation/howto/maintain-git.txt:

- 'maint' branch is used to prepare for the next maintenance
   release.  After the feature release vX.Y.0 is made, the tip
   of 'maint' branch is set to that release, and bugfixes will
   accumulate on the branch, and at some point, the tip of the
   branch is tagged with vX.Y.1, vX.Y.2, and so on.

Сведений о том, как поддерживать более чем одну серию maint-релизов я там не нашёл.