Breeders and retailers can pretty much call anything whatever name they want. I think in most cases, Platinum Whatever is a favored phenotype of a particular strain. Recently, I was in a California dispensary looking at clones, and from the same producer (Medicinal Organics) were trays of Girl Scout Cookies and Platinum Cookies. The trays were nicely labeled and contained the genetics of each, which were identical. Even though the Platinum cut was priced $2 higher, the budtenders could not explain the difference.
Platinum Girl Scout Cookies, and Platinum OG, are two very real strains, and not just fancy names made up by dispensaries. I can't say exactly what the parents were crossed with, as it seems to be a well guarded secret, but both are considered by many to be better than the originals.
The main difference between Girl Scout Cookies, and Platinum Girl Scout Cookies, is the yield. Platinum yields better than GSC, but then again, GSC is a notoriously low yielder to begin with.
Here's a Platinum Girl Scout Cookies that I grew a couple of months ago, very potent, and very beautiful.