MrBond is correct. The warranty on the replacement begins at the manufacture date of the original.
It makes perfect sense for a manufacturer to do that. The drive may very well have failed due to causes beyond their control, for example, a crappy power supply. If they started the warranty period over, the end user could conceivably have free drives for the rest of their life simply by killing it near the end of each new warranty period.
Russ, NCNE