What exactly is the “chiddush” of Motzi Shem Ra?

Question

TL;DR (please see below for a longer, detailed explanation)

Question: What exactly is the chiddush (novel concept) of Motzi Shem Ra?

• a) Is it that if Motzi Shem Ra about a naarah meorasah (consecrated maiden) turns out to be true, her punishment is stoning AND NOT strangulation.

OR

• b) A person who fabricated his Motzi Shem Ra claim is given TWO punishments- lashes and a fine.

OR

• c) BOTH...? Something else?

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Longer Version:

1) The chiddush is that if Motzi Shem Ra about a naarah meorasah is true, she is stoned (instead of being given the punishment of strangulation)

Rambam, Hilchos Issurei Biah 3:8: (see also Ketubot 45a)

דִּין חָדָשׁ יֵשׁ בְּמוֹצִיא שֵׁם רַע. וּמַה הוּא הַחִדּוּשׁ. שֶׁאִם נִמְצָא הַדָּבָר אֱמֶת וּבָאוּ עֵדִים שֶׁזִּנְּתָה כְּשֶׁהָיְתָה נַעֲרָה מְאֹרָשָׂה אַף עַל פִּי שֶׁזִּנְּתָה אַחַר שֶׁיָּצְאָה מִבֵּית אָבִיהָ וַאֲפִלּוּ שֶׁזִּנְּתָה אַחַר שֶׁנִּכְנְסָה לַחֻפָּה קֹדֶם בְּעִילַת הַבַּעַל סוֹקְלִין אוֹתָהּ עַל פֶּתַח בֵּית אָבִיהָ. אֲבָל שְׁאָר נְעָרוֹת מְאֹרָסוֹת שֶׁלֹּא הָיָה לָהֶן דִּין הוֹצָאַת שֵׁם רַע שֶׁזָּנוּ מֵאַחַר שֶׁיָּצְאוּ מִבֵּית הָאָב הֲרֵי הֵן בְּחֶנֶק כְּמוֹ שֶׁבֵּאַרְנוּ

There is a "chiddush" (ie new law) that applies to a person who spreads a malicious report about his wife. What is this new law? That if the slander is true and witnesses testify that she committed adultery while she was a consecrated maiden, even if she committed adultery after she left her father's house and even if she committed adultery after she entered the marriage canopy before she had relations with her husband, she is stoned to death at the entrance to her father's house. Other consecrated maidens concerning whom a malicious report was not spread are executed by strangulation if they committed adultery after they left their father's home, as we explained.

OR

2) A person found to have fabricated Motzi Shem Ra is given lashes AND also has to pay a fine (ie this is the only instance in the Torah where this is so-- we don't invoke the usual principle of "kim lei b'drabba minei")

Rambam, Hilchos Naarah Besulah 3:1 (see also Ketubot 45a-46b)

הַמּוֹצִיא שֵׁם רַע עַל בַּת יִשְׂרָאֵל וְנִמְצָא הַדָּבָר שֶׁקֶר לוֹקֶה שֶׁנֶּאֱמַר (דברים כב יח) "וְיִסְּרוּ אֹתוֹ". וְאַזְהָרָה שֶׁלּוֹ מִ(ויקרא יט טז) "לֹּא תֵלֵךְ רָכִיל בְּעַמֶּיךָ". וְנוֹתֵן לְאָבִיהָ מִשְׁקַל מֵאָה סְלָעִים כֶּסֶף מְזֻקָּק. וְאִם הָיְתָה יְתוֹמָה הֲרֵי הֵם שֶׁל עַצְמָהּ:

When a person issues a slanderous report about a Jewish maiden, and the matter is discovered to be false, he is punished by lashes, as [Deuteronomy 22:18] states: "And he shall be flogged." The warning [for this negative commandment] is derived from [Leviticus 19:16]: "Do not go about as a slanderer among your people."

He must also give her father 100 sela'im of pure silver. If the girl is an orphan, the money is given to her.

Answer 1

The answer (would appear to be) is that the chiddush from Motzi Shem Ra is that she is stoned.
(ie part one of the question)

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^{As @LoAni was first to point out in the comments and subsequently echoed by others}
There are two (!) separate and distinct chiddushim that can be learned out from the episode of a Motzi Shem Ra..

Chiddush #1 - re: Motzi Shem Ra

• Usually: if a naarah meorasah commits adultery, she is given a penalty of death by strangulation
• Chiddush: is that if it turns out Motzi Shem Ra told about a naarah meorasah is true, she is stoned (instead of being given the punishment of strangulation)

Chiddush #2 - re: k'nas

• Usually: if a person commits an action that requires two punishments, we follow the principle of "kim lei b'drabba minei" and only one punishment (the more severe one) is administered.
• Chiddush: A person found to have fabricated Motzi Shem Ra is given TWO punishments! lashes AND he also has to pay a fine (ie this is the only instance in the Torah where this is so)