They even have some flights which go out as a Jetstream 41 from SOU and the same rotation returns as an ATR72 - it does that five days a week. If they've got a magic handling agent, maybe that's where the extra ATRs are coming from! Quite impressive. As long as they don't reverse the spell one day and you send an ATR72 and get a J41 in return....
Is there not a question that whatever any airline has on sale at the moment for the coming winter (routes, frequencies, equipment) is rather aspirational versus the reality of what might actually happen? I don't think Eastern would be alone in that. Loganair's schedule still has loads of ATR72s scattered around too, and BA still has high frequencies showing on a lot of routes that are hard to imagine happening.