if you still have a working key, they can make a copy for you,
other thing is... its easier to loose anything that you`ll leave in the car, than loose it and have to replace a convertible top or part of the dashboard because of the thieves...
I had the door lock cylinder out of our '84 Spider but still couldn't find a 'key code'. It is supposed to be there somewhere...
I did have one key for door & ignition but couldn't find key blanks locally. There are 4 possible door key blanks, BTW.
I ended up contacting Keys 4 Classics, emailing them a close-up photo of my keys and they made copies from the pictures - worked perfectly.
I did not have a door key for our '78 MGB. I drove the car to a locksmith. He had a blank that fit the lock and then made a key for the door - took about 5 minutes and he didn't remove the locks - just inserted the blank key and 'read' the marks made by the lock cylinder to cut the key to shape. And that 5 minutes was not rushing at all!