Bung: IIRC the rumour was that Ford Cortinas only had about 6 different keys. There were numerous stories of people taking the wrong car home from the supermarket. English cars usually had the key number marked on the ignition switch. Some garages would have large key panels with about 20 keys of each combination. It was obvious that keys weren't unique.
Some time ago when a neighbour locked themselves out and had to call a locksmith, who immediately produced a key and opened the door for them, the locksmith said there were only seven types of warded house keys in use in NZ and it was just a case of pulling out the right one to get in. This explains why I was able to use one of the keys from Father Neb's accumulation to open a basement lock for which the original key had been lost.