I have never, ever, heard somebody refer to "actions performed prior to smashing the prism" as "aftercore", since, until you have smashed the prism, you have not "completed" the run, and whatever arbitrarily large number of turns you spend doing something else are still "in run".
And since it is "smashing the prism" in an Avatar-type run that forces you to change to one of the standard classes and lose all the powers and benefits of the class you had while you were "in run", that is pretty much the only thing we could be talking about in this case.