FT_ListDevices will return the number of devices connected (open or closed) when the FT_LIST_NUMBER_ONLY flag is set.
However, FT_ListDevices will only return serial number or description strings for devices connected that are not open at the time of calling the function. This means that if one device is connected and open, FT_ListDevices will not return any string information.
If two devices are connected and neither is open, string information on eachof the two devices will be returned. If two devices are connected and one is open, string information for one device will be returned.
If serial number or description strings are required from an open device, use the FT_GetDeviceInfo function instead.