It's a Seagate desktop backup plus, bought brand new. The weirdest thing is that they have different warranty expiries too.
Already went through the RMA process up to the point of sending it off tomorrow after data recovery, and just realised that the serials are different.
Is this normal, or will it be a problem?
Normal. The serial on the enclosure is what counts. In my case, the serial on the drive itself had no warranty.