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Maybe a dud batch like others said. Or what else could it be....
What's your sizing method... The horizontal crack looks to all be in the same place....

Interesting, the top case has a bright ring at the neck shoulder junction like it was turned, or a thickness was cut from there. (But obviously not)
The others arnt just a straight split but a split...

Have you turned them.... If so how thick are they?

It's very hard to give advise.
If you read the amp anealing site you will see colour or time means bugger all as different brass gives different results. The only sure way would be if someone is...