Funfact: in the past Ford and Volkswagen had only a number of different variations for the coding of the physical keys. So that you could open and start several cars with the very same physical key.
I assume that this was also true for other brands.
Many fleet vehicles are still this way. The 1284x key, for example, can open a surprising number of things including many older police vehicles.
A few hundred dollars more on Amazon will net you a magic keyring that can open a surprising number of vehicles, buildings, control systems, and vending machines.
If you're into that sort of thing check out Deviant Ollam's physical pentesting videos on Youtube.
That's a good start. To do better you'll need to do some reading or watch a ton of youtube videos to identify the keys that will get you the most bang for the buck.
I think mine has something like 20 keys on it now, and it will open a truly surprising number of things that it shouldn't.
This happened to me! Friend had a similar car and at night they went to mine and the door unlocked but the car wouldn't start. The door only had a few pins it checked while the ignition used every pin. We compared our keys and sure enough one part of it was the same.
OBS Ford F-150s do this and it's not common knowledge even among enthusiasts. The back 4 pins work the door, the front 6 or so pins work the ignition. A common problem is that the ignition barrel keyswitch dies and you have to replace it, but then you have separate keys for the door and ignition. I took the new ignition key to a locksmith and had him copy the 4 back pins from the factory key, and I was back to a single key!
I had a similar experience once when I drove a Prius. Walked out of the grocery store, hit the unlock button, got into my car, then wondered why the seat was too far forward - before realizing it was not my Prius.
My mom amd my friends mom both drove toyotas, completely different models and many years apart. By coincidence the key for my friends moms car worked for my moms, for unlock and start, but, my moms could only unlock the other one.
Fun fact: the same applies to common household locks. If you take your household key and try all the same-brand locks in your neighborhood (~50) you'll likely find a match. Don't actually do this, your neighbors will think you're causing trouble.
In the 1970s, I unlocked the door on what I took to be the family VW Rabbit and got behind the wheel. It turned out that the ignition lock was fussier than the door lock, and I discovered my mistake without driving away.
Same thing happened to my Dad when he took us to Disneyland in the 80s. About the time the rental car agency was sending out the spare set of keys, he noticed the items in the backseat weren't ours.
I have a Honda from the late 90s which behaves in a similar way and whose ignition is also fussy but only to a point. With enough wiggling, a key from a different model from ~10 years prior will also start it.
I assume that this was also true for other brands.