They are known to also go by the manufacture date warranty, so if you buy a model that was released not long ago, you're pretty much guaranteed to have a good chunk of warranty left.
Thing with that statement is that different companies may have different policies. And is probably why OcUK state any reference to other warranty is to be ignored with B-Grade items. So if you want to know for a fact, inquire from the manufacturing company itself.
Don't quote me but I think Gigabyte and EVGA are two known to currently honour manufacture date warranty in case of B-Grade. I believe I have read statements from their Reps about it. In fact if the thread is moved to the Graphics Card forum, they may see it and confirm.