> That, and the HISTORY file contains a release date for 26.2 as well.

It's the same problem. Suppose we update HISTORY to the date of RC1.
If RC1 becomes Emacs 26.2, the date in HISTORY is correct; otherwise
we will commit a modified HISTORY with the release of the next RC.

Just a note: with my proposal there is always a difference between 26.2-rc1 and 26.2 (the names), so the history date would change as well.

Philippe