How is a jigsaw puzzle able to make unique fitted pieces?

Making jigsaw puzzles used to be a cottage industry. Many puzzles were cut at home by experienced people using a jigsaw. They cut according to certain patterns (there were several basic cut styles). Because they were hand-cut, a duplication was possible but unlikely. Some were completely random and some followed a basic structure such as the four-sided pieces we mostly see now. To duplicate, you’d have to match on all four sides.

In the U.S in the 1930s, there was a wild jigsaw puzzle boom and a lot of work for the cutters. Puzzles were circulated by lending libraries. In those days there was no picture on the box, so you were on your own.

Now they’re done by machine, and so the template can be scrutinized, checked and rechecked for unique pieces. Many puzzles can have the exact same cut. I knew a couple years ago who were jigsaw puzzle fiends. They were so familiar with the arrangement of pieces on the very popular Springbok puzzles (cardboard, but very well made, with great pictures) that they could recognize individual pieces right away and knew where they went. Sometimes they would turn a puzzle over and solve on the blank side just for a challenge.

My favorites are the beautiful wooden puzzles made by Liberty Puzzles. Their pieces are not cut according to the familiar innie-outie-innie-outie interlocking pattern. They are all unique and look random, except for the “whimsies,” the pieces that have a recognizable shape—a flower, a woman in 1890s dress with a parasol, a man on a unicycle, a wheelbarrow—or geometric regularity.

The last few puzzles I’ve put together have had more than one piece fit in the same spot. It isn’t a problem if the coloring doesn’t match, but that’s often not the case. I’ve given up on jigsaw puzzles because this is a new thing I’ve never encountered before. If the puzzles are designed and cut by computer, how hard can it be to make sure there aren’t duplicate pieces?