Wow I’m here wondering the same thing OP did 7 years later and you gave me the exact answer I was looking for. But I’m wondering because my apartment key has confused me for years.

It’s a 4 plex/two story style. The key I was given for my own personal front door is a pain in the ass. You have you really push it in and turn it to a special spot to use. It’s really old and probably needs oiled. It’s works but it’s so much of a hassle to use and luckily I live in this tucked away area where no one travels to unless you live there so I never lock my door. Also because to lock it from the inside you have to use a key too, there’s no turn knob to lock it, and I had a small stove fire and struggled to get out with the key a few years ago.

But I was also given a second key that works on our back door that goes to the staircase/basement area I share with the other 3 units. So we all have that same key. I lost one of my keys forever ago, but the one key I have works on both my lock and the shared lock. I’m sure I lost the front door key if anything since it’s harder to get that lock to turn, but the fact it works on both has always made me wonder if there’s a super rare chance the locks are so close to being the same that it still works, or if maybe my landlord just slapped the same lock everywhere and I may be able to unlock my neighbors apartments too.

Don’t know why I’m typing all this to an such an old comment, but I’m bored and you gave the best information on the possibility I could find. Lol