alt Hacker NewsAstra > 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.