How can Bukhari's narration in "Al-Adab Al-Mufrad" – that the Prophet (peace be upon him) witnessed the Hilf al-Mutayyabin – be reconciled with what is known, that he witnessed the Hilf al-Fudul?

The Prophet (peace be upon him) witnessed Hilf al-Fudul (the Alliance of the Virtuous), and he called it "Hilf al-Mutayyabin" (the Alliance of the Perfumed Ones) because the tribes participating in it had previously concluded the Hilf al-Mutayyabin. Hilf al-Mutayyabin was before the birth of the Prophet (peace be upon him), whereas Hilf al-Fudul was witnessed by the Prophet and took place in the house of Abdullah ibn Jud'an twenty years before his prophethood. In it, they covenanted to return excess possessions to their rightful owners and not to support the oppressor against the oppressed.