The issue was raised regarding the producing of mamzerim through the giving of an invalid Get. Isn't this really a non-issue since if the mamzer is not revealed - there is no prohibition of marriage and therefore everyone is presumed to be kosher?
Edios (8:7): Rabbi Yehoshua said, I have received a tradition from Rabban Yochanon ben Zakkai who heard it from his rebbe and his rebbe heard it from his rebbe as a halacha l'Moshe m'Sinai (Tradition given from Sinai) that Eliyahu will not come to declare unclean or to pronounce clean, to put away or to bring near. But rather he will put away those brought near by force and to bring near that who have been put away by force. The family of Beis Zerephah was on the other side of the Jordan and Ben Tzion put it away by force. And there was already another family there and Ben Tziion brought it near by force. For such people Eliyahu will come to declare unclean or to pronounce clean, to put away or to bring near. Rabbi Yehuda disagreed and said Eliyahu will bring near but not put away. Rabbi Shimon said that will come to resolve disputes. The Sages disagreed and said that Eliyahu will neither come to put away nor to bring near but rather to make peace in the world. As is stated in Malachi (3), Behold I will send Eliyahu the Prophet to you... And he shall turn the heart of the fathers to the children and the heart of the children their fathers.
Bartenuro (Edios 8:7): It is a halacha L'Moshe m'Sinai that G-d showed Moshe at Sinai... that Eliyahu will not come to declare unclear or clean or to make distant or bring close to clarify doubts concerning which individual are problematic who have been mixed in the family - but these doubts will be left and they will be kosher in the future. The halacha is that a family which has posul individuals successfully mixed in and unidentified- they will remain unidentified as posul. ... those families where posul individuals have been successfully mixed in and they are not know as posul individuals but are presumed kosher - Eliyahu will leave them that way.
However the following claims that the prohibition of revealing information is only when it is based on rumors - but not on the testimony of two witnesses.
Chelkas Mechokek (2:5.9): One who knows that there is a mamzer is not allowed to reveal this information – But it is stated in Shulchan Aruch (EH. 2:3) that two people had testified that a family has a mamzer or challel. How can they do this since they are violating the halacha of not revealing this information? However saying they shouldn't testify also presents a difficulty since we pasken in this sif that if there is a doubt whether there is a mamzer in a particular family that someone who marries a member of that family needs to get divorced – so why isn't it a mitzva to reveal this information because today or tomorrow witnesses will come and testify that there is a mamzer in the family and consequently the children of this family will be considered sofek mamzerim? A possible answer is that concerning the Ran on which the leniency of the Rema is based, he could be talking about a case where it is not clear that a member of the family is actually a mamzer – but merely that there is a rumor. Perhaps it is only such a case where the Ran is saying that there is no need to reveal this information except to modest people [who won't spread the information]. However when two witness know for certain that a mamzer assimilated into this family it is very difficult to claim that they should not testify since the children of this family - once the information becomes public that there is a mamzer who is mixed into this famly –will henceforth be sofek mamzerim.