פירוש על קידושין 102:11

In the mishnah, the father at one point knew which daughter he was betrothing. At the point of betrothal, the kiddushin could have been followed by intercourse. Later, he and the husband became mixed up, and this is why three of the girls are prohibited. In other words, the kiddushin were done properly, but the identity of the betrothed girl was subsequently lost.