If you're asking about the names then it's really marketing/branding. A tessar is both a design and a Zeiss lens. You might have gotten away with copying the design [The Xenar I think is a tessar] but you couldn't use the name. That's the reason some companies continue to use older names. If they use the name they retain the rights to the name. Somebody mentioned Kodak was calling the lens on a disposalbe camera the Ektar.