Every remote 59XX phone I've seen is an IP-KT, but I've got one site where it currently shows as an IP-SATT. An older database shows it as IP-KT. It's working fine but I wonder what would make it change and what's the difference?

IP-SATT means the extension is programmed as a Simple Attendant station, which doesn't really mean a whole lot with an ECS. About all you can do from the attendant is change system time and turn some hunt group features off and on.