Once had a father in law who was a locksmith. Would go with him on some lock out service calls This was in 60's. GM cars he had a key ring with a very large number of keys that he would try until one would be jackpot. Somewhat forget what he did with Fords,,,,perhaps the owners if locked out were not interested to pay to gain entrance and just walk away from them.

Mopar's he would insert a blank key, twist and shake it about to make slight impressions on it, remove it, file impressions a bit and try again until lock opened.

He called it to impression the key. Always worked, but he preferred locked out GM's.