I've thought about this strand for a few hours, so I put it to a differential diagnosis.
On the merit side, 4.9mm Tahitian pearls are generally too small for bead culture. On the other hand, it's not unlikely either. To that end, a half point is scored to each natural and cultured origin.
A large diamond of several carats accents the piece, hence adds substantial value but does nothing to support natural origin of the pearls.
There is no evidence of color enhancement, but no point is scored because the lack of post harvest treatments are not unique to origin.
In the absence of other information, this is where the merits end.
On the demerit side. Other than the stated article, I could not find a single link, image or article describing this strand nor it's supporting documentation. I'm sure there's something somewhere, but definitely not widely known nor available for review.
Fine strands of natural pearls require an enormous pool for selection criteria. Two hundred and eighty nine pearls matched to a quadruple graduation would in all likelihood come from a pool of naturals greater than one hundred times that volume. To suggest there's a harvest of natural pearls in excess of twenty five thousand pieces multiplied by the 1:10000 average likelihood of even finding a natural seems like a stretch. That is approximately 250,000,000 oysters folks! A mathematical improbability, no less a brutal slaughter of Maoist proportions for a single vanity piece. Although I'm not wholly aware of Tahitian laws, I'm inclined to think they'd still need to be inspected and certified before export. Even if they were amassed from traditional harvests over decades, they'd still need to be brokered and graded by someone.
Think about it for a moment. Would anyone accumulate $5.1M worth of pearls, yet not lend their name to it?
Even small commercial operations, Cortez, Kasumi et al require multiple years of production to manufacture a single strand. My collection consists of several thousand pieces, but I'm hard pressed to match pairs, no less entire strands.
Incidental spontaneous pearls found in farm reared inventories cannot be deemed natural. While some may be, no one would suggest others could not be formed by stresses from harvesting, relaying, handling etc. It makes no sense to destroy a perfectly good graft candidate in the one in the ten thousand chance of finding a natural pearl.
The Swiss Gem Lab is reputable for the most part when it comes to other gems. However a drilled pearl is a destroyed pearl in scientific terms, hence cannot with one hundred percent certainty determine the origin of a pearl.
In this analysis, demerits far outweigh merits.
My heart of hearts tells me, this is a mixed strand at best, consisted of few (if any) naturals, some keshi and largely non bead grafted cultured pearls.
