We always go by the fingernail rule in the shop. If you can catch a crack with your fingernail, they need replaced.
Like chris said, check the date, as new tires might actually be retreads on an old casing.
Also, your first picture shows a tires that's a prime candidate for a delamination issue fwiw.
If this thing was just local usage, I'd likely not fret about it. But with a cross country trip in the future, I'd be cautious and replace them.
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