Some similar apps shows Carrier Aggregation information from hidden Android API - same you can see by calling to *#*#4636*#* -> Phone Information and scroll down. We have desired not use this information because it's unreliable and do not tell witch cell exactly connected (SCELL do not report Cell ID example, only PCI and PCI value could change). That's why CM App only show LTE+ when connected to another cell. Also depends phone what combinations it support so different phones will report different scell bands so it's impossible show reliable information.