I would not worry about it unless the new growth gets the spots. But that is me, I don't worry about every imperfection , but then I get unpleasant reminders and consequences when the imperfection was something I should have minded.. The old leaf is a source of food for the new leaves and will slowly become a old corked stem supporting several new "branches" usually coming from the base. The old growth will not grow itself. Many people cut it back after the new growth start to appear in a crowd. I might consider giving these plants a bit more room.

thanks, wantonamara!