Astra > Sol > Terra > Luna seems clear enough to me
Leopard (10.5) and Yosemite (10.10) both came with clear version numbers
Model X and Model Y are siblings which do not have a clear hierarchical relationship
Gemini 4 Carbon and Gemini 4 Argon are rather difficult for me to tell at a glance
Confusingly, Carbon is another model in the same size class as Argon. Every other lab would have just called it Gemini 4.1 Argon.
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Ideally, Google would have run with:
Argon > Neon > Helium
That would have been the noble thing to do.
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