It is possible. A single pearl would have to be submitted to the lab for certification. The certification isn't cheap, so that's why not many do it unless requested. The end result is that a single certified pearl is more expensive than half of a pair.
The GIA fee schedule I found charges by carat weight, not mm size. It's $60 for a very small pearl, under 3 carats. A larger pearl will weigh more. If I'm reading it correctly ...
When you are looking at single pearls, you can ask the vendor for the weight.
My guess is a 9 mm Tahitian would be $100 since it's bead nucleated, but you'd need the weight to be sure.
I would think that most people requesting GIA review are sending in multiple pearls, strands or bags, so charging fees by weight would be easier for the GIA.
The GIA prices for a single pearl are probaby by carat weight, because they only get natural pearls to evaluate, and naturals are done by carat weight, not mm size. I think GIA may never had a single cultured pearl sent to them.
Single natural pearls -- yes. Undoubtedly many single natural pearls are sent to GIA for certifcation.
She said: "I think GIA may never had a single cultured pearl sent to them." (bolding mine). "Single" as in just one pearl. As in, a person sent in just one cultured pearl for certifcation. And she is saying maybe that hasn't happened.
I think you misundertood the use of "single" here.