OSX Yosemite is the brand. 10.10 is the product name.
No, OS X is the brand. You don't change your brand name every year, the one that's consistent over time is the brand.
Yosemite is the product name, product names can change any time and it is usually what customers know it by.
Another example, Windows is the brand but Vista, Windows 7, and Windows 8 are the product names as well as the version.