When you go to System, Administration, Create usb startup disk, it expects an
ISO image file. If your ISO is downloaded then it is likely them most recent
release which means that it will need to be updated, because it won't be any
different from the one installed from CD. If you create your own ISO image then
it can be anything, including one created from your current installation. This
is then a two step process instead of one. This also leads to the inevitable
process of how to create an image from your current installation. I am not sure
if the user wants to go that far, but if he does perhaps he can ask first.

There is no such thing as a dumb question, only dumb answers.