What is the difference between "Narrated by the Two Shaykhs" and "Agreed Upon"?

"Agreed upon" (متفق عليه) and "of sound authenticity" (على صحته) are two phrases that carry the same meaning, referring to the agreement of the two Shaykhs (Bukhari and Muslim).

Scholars differed on whether what the two Shaykhs narrated conveys definitive knowledge (علم قطعي) or probability (ظن). Imam Al-Suyuti, Ibn Al-Salah (definition), and the majority of Shafi'is, Hanafis, Malikis, Hanbalis, Ash'aris, Hadith (definition) scholars, and the Salaf believe that it conveys definitive knowledge, due to the Ummah's acceptance of it. Whereas Al-Nawawi and Ibn 'Abd Al-Salam are of the view that it conveys probability unless it is mutawatir (transmitted by multiple independent chains). As for Ibn Hajar Al-'Asqalani, he believes that what the two Shaykhs extracted conveys certainty, not merely due to the multiplicity of chains, but because of the accompanying circumstantial evidence such as their eminence and the scholars' acceptance of their books. Scholars are unanimous that the two Sahih (definition) collections possess a distinction in authenticity and that their hadiths are the soundest of the sound.