In the olden days too, women had sacrificed their Chastity under various conditions.
Innocence in the initial stage and later, necessity prompted Kunti to accept husbands of divine celebrities other than the human husband ordained for her. Impersonation impelled Ahalya to fall into the hands of a celestial celebrity who was lured by her pristine beauty. Jabala became polyandrous due to occupational hazard combined with abject poverty. Ambika and Ambhalika, were forced by their mother-in-law, Satyavathy, to accept Vyasa, as their husband for the purpose of creating a heir for the crown.
Such incidents would have happened earlier too. Human weakness and necessities, like many other things, have no dates.
So, it was therefore natural for the Rishies to expect the recurrence of such things in the future too and it was in their immense wisdom and practical outlook that they ensured that our pindadhanam, offering to manes reach our biological father.
They never had in their mind my mother or your mother and therefore let us not become emotional while reciting the above mantram. Mantras are common for all, including Jabala Satyakama and Siva Perinkulam.