Are orcs immortal??

[pandora]

Just because orcs like Shagrat and Gorbag reminisce 'good old times' doesn't mean they have actually witnessed them.

Read the section in question. Either they saw them or they are Orc Lore Masters who have studied their race's history. Doesn't seem very in-character, does it? Their attitude to the Nazgul as newcomers simply doesn't ring true if they have a life-span akin to Men.