Without arguing either the historicity or the historical accuracy of the midrash of Eleh Ezkerah, the 10 Martyrs, I am wondering about the details of the story as told. According to the version on the Chabad website, the ten are asked
What is the law with regards to he who kidnaps a man from the Jewish nation and sells him [into slavery]?” The rabbis replied that Torah mandates that such a man be put to death. “If so,” continued Turnusrufus, “where are your forbearers who sold their brother into slavery? Had they been here, I would have prosecuted them before your eyes. As for you, accept the decree of heaven, for since the times [of the 12 tribes] there have never been 10 sages of your stature [alive at one time]. Take upon yourself to die in accordance with your law; for Joseph the son of Jacob was kidnapped and sold by his 10 brothers, and their punishment has never been exacted.
What troubles me is the rashi on Bamidbar 7:22 which references the medrash Rabba and reads
One young he-goat: to atone for the sale of Joseph, about which it says, “and they slaughtered a kid” (Gen. 37:31).
In terms of the narrative, the Rabbis had a perfect answer -- the kidnapping was atoned for by the specific offerings in the desert. Now, while God might have intended them to be killed for other reasons and the voice from behind the curtain might have intended things to end as they did, it seems that the rabbis in the story should have objected to the charge as having been resolved generations before. However, it seems that according to the language of the Eleh Ezkerah, the required punishment is death so the claim in rashi, that an offering atoned, could not be true.
Is the rashi/M"Rabbah wrong or did the composer of the Eleh Ezkerah ignore the fact for literary reasons, or is there another halachic wrinkle involved?