Nie chodzi o obecne przypuszczenie dot. stanu przeszłego, ale raczej o przypuszczenie dot. czyjegoś wyobrażenia na temat przeszłości. Spróbujmy z innym zdaniem:
Someone has stolen a diamond.
If Marry were the thief, she wouldn't tell anybody about it.
If I had stolen the diamond, I would have left the country.
ale wątpliwości mam z poniższymi:
If you father thought that (you had stolen?) the diamond, would you tell him about it?
If your father thought that (you were) the thief, would you deny it?