Not getting an invitation in the "first wave" does not necessarily mean you won't get one eventually. I am a coordinator, but I have no back-up/assistant as some programs might and there are many other things to do besides set up interviews. 🙂 In order to keep things manageable and ensure we fill our earliest dates first, I send invites in smaller groups with limited date choices. If someone absolutely can't make it on those date choices I will inform them of other later dates. But remember, just as you want to visit as many programs as possible to find the best fit for you, programs want to interview as many people as possible and not have gaps in the schedule. When we have cancellations we will then offer those spots to more people, even if it is very short notice, just trying try to "fill as we go" so to speak. And sometimes those last-minute fill-ins turn out to be the gems of the program! So try not to get too discouraged... it's still fairly early for some programs.