Yes the tumbler plates are numbered, but that is to indicate the depth of the corresponding cut in the key.
That allows the manufacturer to cut a key to a numeric code, and then know what tumbler plates have to be inserted to correspond to the key they just cut.
If they make a cut on the key at the first tumbler position to a depth of 4 for example, then the assembler knows he has to insert a #4 tumbler at that position. And so on for the rest of the tumblers.
You will notice that the number corresponds to the preset depth of the tumbler, not which position it should be assembled into.