You seem to have some facts confused, Howard Marks never bred Cannabis, he was possibly the most successful smuggler of hash and marijuana ever. Marks has since allowed Shanti to use the alias Mr. Nice as the company name but this does not make Howard Marks a breeder. Shanti is the original breeder of White Widow and he created it towards the mid nineties while starting up Greenhouse seeds with Neville and Arjan. As far as I have found Shanti was not using any stock from America and the strain was definitely bred in Europe. I don't believe Shanti ever did any work in the states. Same with Neville, his famous SSH also was created while starting up Greenhouse, and he never bred out of America. Neville was actually quite responsible for bringing much of the foreign seed stock to Europe, he actually traveled the world over looking for the best seeds to work with.
The strains that originally made its way to Europe from Cali were Skunk, Haze and Northern Lights, and these strains still make up much of the genetic backgrounds of strains all over the world. While not American landrace strains, those three are distinctly American varieties. Jamaica at this point probably does actually have landrace strains. Enough generations of specific genetics have been grown in Jamaica to make them uniquely Jamaican even though the original seed stock is from other parts of the world.
As for OG, well this topic is just kind of a mess. It is a variety that definitely came out of America but it is near impossible to trace its original history so the genetics for it could be from anywhere. Not to mention OG comes directly out of the Chem line of genetics, which are genes originally discovered in America. But OG is getting harder to trace as just attaching the name OG to any strain brings its value up, so cash croppers will sometimes add the moniker to strains that have no genuine OG genetics in them. Not only that but there are several varieties of verified OG that come from different sources, and while all similar in traits, each is still unique. Then there is the constant out-crossing the verified OG's even further confusing the issue. Raskal is using a verified cut he has had for many years at this point, and his crosses seem to be of premium quality and I have heard little negative talk about his strains.
I hope this helped clear up some confusion.