I'm not sure where the Key Code Number is on a Honda. However, with that
number, the thief can just go to a professional lock smith and he will look
it up in a table of key cuts.
I know that some older VWs had the key code on the right door lock assembly
that is easily removable once the door is opened.
On a Nisson I had in the '80 the key code was on a tag that had been left in
the glove box.
Often the key code for the ignition switch is stamped on the cylinder and
once the trim is removed from the column, it just takes a mirror to read the
One of the advantages of having different keys for the doors and ignition is
to prevent a key being made for the easy removeable door cylinder that can
be used in the ignition.
Then of course, there is always the more obvious possiblity, that someone
else still had a key to your car. Maybe a friend or relative of the previous
owner. However, then, why would they have jimmied the window.
Bottom line, I think they opened the door, removed a lock cylinder and made
a key to fit the whole car.
My experience and opinion, FWIW