I will say I bought two HDDs from Amazon just in November, and they were new. I just validated that as well. I purchased directly from Seagate on Amazon.
This is the usual reminder that the seller you select on Amazon is no guarantee about who supplied the product when it's fulfilled by Amazon.
Unless the seller has opted out of Amazon's inventory commingling, their products got binned with everyone else claiming to sell the same product and you got one at random.
If Seagate sends a box of Seagate Exos 16TB drives in, Amazon puts them in bin 1234.
If Joe's Computer Shop sends their new, authentic Seagate Exos 16TB drives in, they get put in bin 1234.
If Sam the Scammer sends in a couple of "new Seagate Exos 16TB" drives in that are really just reflashed 80GB drives from the 90s, they get put in bin 1234.
You order a Seagate Exos 16TB... you get one from bin 1234.
The only way to avoid this is to contact the seller beforehand and see if they've opted out of the commingling. But at that point... very likely easier to just buy elsewhere.
I will say I bought two HDDs from Amazon just in November, and they were new. I just validated that as well. I purchased directly from Seagate on Amazon.