I think that they probably don't have code names because everyone knows (or hopes) that Apple is working on minor bug fixes and updates whereas the big releases have all new features that they like to keep quiet, thus the codename.
Correct. 10.1 through 10.1.5 are still "Puma." 10.2 or 10.5 or whatever it will eventually be is "Jaguar," and it will be Jaguar until the next major revision... so 10.2.1 is still "Jaguar." 10.2.9 is "Jaguar." 10.3 is something else.