Does anyone of you guys have an idea what series this is?

I've known this HDD type almost since it was first produced in about 2006, and in all these years I have NEVER encountered any drive that had a ser# starting with the above code (mine starts with S0ZLJ1DP7...) until one month ago.
Bought this off an auction site...

P is the 2007 production line (L would be the 2006 one), so P7 is July 2007.

OK, but why doesn't it start with the typical S0AXJ... code? What (internal) difference does the different code make?
Unfortunately I can't google that myself, because when there is no gap in the serial #, Google unfortunately won't match on partial serial numbers...(tried that before, of course.)