thats simple, its no different then under MS Windows. the device is NOT flagged by any special means and is just mounted in a willy nilly order so to speak. What ever device goes live first is sdb, then sdc, etc...
Just think about USB Printers in Windows. Its installed, its running, but god help you if you unplug it and plug it back in, you will be prompted to install new hardware and start amassing multiple copies of the same printer and none but the last one will work.
Or you plug your USB drive into Windows, today its drive letter E:/ tomorrow you have an other USB device plugged in, you plug in what was E yesterday, but today its F:/
its all the same.
if you want to get around that, the a few things need to happen.
1. disable the automagical mounting of USB devices
2. create a script combined with labels on the flash drive.
3. mount the specific label to your desired location
4. learn udev rules and customize each device for mounting at specific points into the system
you can also stop using drive letter and use drive mapping:
as each device once formatted is unique.