[jcranmer]

The closest case I recall is that some seed banks were mixing the Monsanto's seeds with other seeds (in a seed vault) and trying to argue that the resulting seed didn't need a license from Monsanto.

Probably the main case that comes up is the Schmeiser case, where Schmeiser claims that his roundup-ready canola came from cross-pollination from a neighbor's field. Schmeiser's account does include the fact that he specifically tested the canola in question and found it to be resistant to Roundup--and subsequently used that in later crops. The court concluded that he had to know that at least some of his crop had the GMO canola, and that his deliberate use of it in the subsequent year constituted infringement.