I don't think a "Top Shelf" Miami has been developed enough to be its own line bred cultivar.
"Top Shelf" is simply what Carol Huddleston labels her Miamis that look particularly promising at birth.
Carol has developed an extremely clean almost Okeetee like look to her Miamis. I would say that they are consistent enough and nice enough to be considered as a type of line bred Miami (think of Reverse Okeetees, Sunglows, ect.. all Amels blah blah), but I would refer to them as Huddleston Miamis. Top shelf just refers to Miamis within Carol's stock. If you buy a "Top Shelf" Mami from Carol, vs a regular Miami from Carol, I think it just is more of a guarantee that the animal will have a very clean silver background and bright red or orange saddles with thick borders.
I hope that wasn't too confusing!
If other Breeders refer to some of their Miamis as "Top Shelf" I haven't seen it.