Believe it or not "fell off the back of the truck" is a lot more common than the jokes make it out to be. I'm not saying for certain that's how it happened, but it is a possibility. You would think it would be harder to do with serial number tracking and such, but once the product transfers from MG control in their distribution centers to the trucking companies, anything is possible... ("Damaged" in transit and written off despite being undamaged, truck in an "accident", etc...) If it is a verifiable accident where the truck trailer is damaged, some shippers are more likely to write off the product inside completely and inform those who had product, then "scrap" all product instead of trying to determine what is undamaged; well "scrapping" involves a certain degree of human reliability to actually "scrap" the shipments... Chances are any serial numbers you might still find on those products (If they haven't been removed or forged) have been written off by MG and therefore will not be honored for warranty.
Again, not saying that's how it happened, but depending on how early MG started pre-distribution of product before actually releasing it, its possible people in the actual shipping chain have had months to get their hands on the stock and wait for an actual release. This happens with a lot of products you find find in "brand new" condition for way less than it should be. (Think "organized crime syndicates" - in the right conditions they can get "control" of entire industries, including trucking/shipping unions.