I'm not certain where I got the idea of making a duplicate key from a code on the key - probably from my collection of Thule keys. I think cars from this period may have come with a code tag attached to the original keys. I had a '71 Porsche which came to me with one attached to the ring. This is probably a legitimate way to do this, but alas, if that existed, it's long gone. Hopefully someone with a better grasp on this can help.

Nowadays, manufacturers keep the key info on record, and can order replacements based on proof of ownership. Did a couple of modern BMW keys this way. Modern Volvo (at least up to P1 chassis) makes it really complex, as they can cut the emergency key on site, but they also need your car to program it to the key. If anyone ever buys a Volvo from this period, and it comes with only one key (as I did), ask the seller to knock $400 off, because that's what the replacement costs. This stuff factors in to why I went back to an older car. That, and maybe it's my lite-version of a mid-life crisis...

As for my tailgate lock - that was totally self-inflicted. I wanted to wash my wife's car, and just as I went outside with the sudsy bucket, she had to leave. So I washed my (fairly clean) car instead. And it froze overnight. I think the little flap that's supposed to keep water out isn't working on that lock. It's better now. So that's my next tip: don't wash a clean car - particularly in winter.