Ten dollars for a graduated strand of vintage akoyas is a terrific find.
The pearl in the stickpin is a curiousity for sure. It's really difficult to examine a pearl from a few photos, but the law of averages suggest it's an early cultured freshwater pearl.
That's not to suggest precisely what that pearl is, but it might give you some idea how difficult it is to definitively determine it's origin. Afterall, there is no evidence of the producer, species, area of harvest or original sale price.
If it is natural, it's not extraordinary, but no less wonderful. Lab certification would certainly increase it's value, but you'd need to weigh that against the cost of doing so.
Wear and enjoy it for it's beauty and mystery.