Ah, http://symfony.com/doc/current/contributing/documentation/overview.html#documenting-new-features-or-behavior-changes seems to be quite clear about all that. The version note should *precede* the new/changed feature (currently only valid for one out of six note in the form reference) and version notes are only removed from *new* doc branches and then only for Symfony version that reached EOL, not EOM. But then you may have to add a version note for a EOL release if you are working on an existing branch like 2.3 and add a missing documention ;-)