I like to understand the term “finished” rather in a life cycle manner. That code needs to be touched from time to time is obvious and undisputed.
But the more interesting question is:
Is there code that works now, but we won’t bother to improve or adapt it and won’t use it ourselves?
An example where we got a statement is the ComponentBuilder, which is used in the old Projucer GuiBuilder, but it is deemed end of life and will rather be replaced completely if at all.
Sounds like the same could be said about box2d according to @RolandMR.
Such information would be extremely valuable to plan ahead!