I had an 86 Honda Civic and have a similar story. I was just getting out of class and heading to work, walked out to my car, started it, looked behind me to back out and realized the stuff in the back seat wasn't mine. Turns out someone had a very similar civic that was even missing the same black plastic strip on the side panel mine was. And my keys worked in their cars.
Now if you still had an 86 Civic, it's highly likely that just about key from any Honda from that same era will open it now. The keys all wear down and so do the tumblers in the locks.