Tell us which old HOTM will come out during that month’s Atlantis event

Everyone knows what heroes in events are coming (with the exception of new events) so that we can gather up gems and prepare our good luck charms, but no one knows ahead of time which old HOTM will be coming out next. For an event that repeats I think it’d be nice to at least know which HOTM will be returning month-to-month (or at least known at the start of each month who will be coming out that month). These aren’t new heroes, just desireable ones, so why all the secrecy?