On a hunch, I pointed a file recovery program at the drive. It didn't find anything, and deep scan will take a full day. That will at least confirm whether it was a used drive fraudulently sold as new, or they really did leave it sitting on a shelf for 3.5 years before I bought it.
If they wrote all zeroes before resetting SMART (which they would have done if they had any brains), the scan won't find anything at all. Seagate drives have a special storage area that records data that doesn't get wiped when SMART is reset, so it's possible to read that to verify the power-on hours, but apparently other brands don't have any way to tell.
I'm the one that mentioned the labeling, but as I said, I've never seen a drive that had two labels in the first place (where would a second one go?). I can't even find any actual images of retail packaging for the enterprise Toshiba drives, and even their own site just shows that plain label on their page for the MG10/11. They do seem to have started using a colored stripe on retail drives to indicate the class, Surveillance, NAS, etc., but I'm not sure there is a retail enterprise version. You can't buy them from Toshiba directly (except in volume by calling their sales department), so I'm not sure there actually is a difference between OEM or retail with them.
There's really only three HDD manufacturers now. Toshiba, Seagate and WD. Everybody else is small brands just rebadging the others and claiming they're "specially certified", or they're refurbishing them or getting B-stock and rebadging them. Hitachi storage was sold to WD, but Toshiba also got some of their tech. Seagate has the largest market share because they're the cheapest and OEMs are happy to cut corners to save a few pennies, because the RMAs cost them less than what they saved (or at least comes from a different budget and appears on a different Powerpoint slide so it lets their sales continue to look good even if a lot of them need replacement), and of course consumers just see price mainly.
WD is the most reliable of the three, although sometimes even they might have a model that is a dud (it just happens less often). With WD, at least in enterprise/datacenter drives, you're looking at much less than 1% failure rates on average. With Toshiba, like 1.5. With Seagate it's 2 or above. Anecdotally, Seagate does seem to have the same lower reliability in consumer drives, on average. Seagate may produce one or two models that have amazing reliability, but then they'll make one that is just atrocious, and with the majority of them just being in a wide "pretty bad" category. WD is consistently "really good", even if they have had one or two "pretty bad" models; they just don't release anything atrocious. Toshiba seems to be consistent within a wide "fairly good" category. I've also been happy with WD's RMA process in the past, a little more than with Seagate's, but I've never used Toshiba's.
If you're using a single drive to store your data, you'd want WD (even if you're backing it up somewhere, simply to avoid the hassle of a failure and having to restore data). If you're using multiple drives in RAID, you can go with Toshiba or Seagate, depending on how tolerable a failure would be. If it's just RAID1 with two drives, Seagate is fine because everything will still work exactly the same if one fails. If it's a RAID5/6 array with any number of drives you'd want to consider spending more to avoid a failure because of the performance degradation of a failure in RAID5/6, and a rebuild is also very intense so perhaps could cause another failure. RAID10 with 4+ drives would also work with Seagate as there's no performance loss with a failure, and rebuilds aren't bad. RAID50/60 aren't as bad as 5/6.