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My understanding is only the early die states showed Cameo coins (not sure of this)
Correct and the cameo contrast would vary. Sometimes even the earliest die states would still only be a modest cameo.
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Some one can chime in and when it happened but somewhere along the line the mint
started etching the die's so that they all have a cameo look and even have developed
a reverse proof where the fields are etched and the devices mirror like.
Intentionally going for the Cameo look started in 1973. Reverse proof was 2006 although some of the platinum coins may have had it earlier.