Short answers, pulled from the story.
The Sanskrit word āgama means sacred work or scripture, according to Monier-Williams' 1899 dictionary. This term refers to a collection of early Buddhist discourses preserved primarily in Chinese translation.
A complete version of the Dīrgha Agama was translated by Buddhayaśas and Zhu Fonian during the Late Qin dynasty in 413 CE. The Madhyama Agama translation occurred under Sañghadeva in the Eastern Jin dynasty between 397-398 CE.
At least four early schools maintained distinct recensions of four of the five Prakrit Sanskrit āgamas. The Sarvāstivāda, Kāśyapīya, Mahāsāñghika, and Dharmaguptaka schools all produced different versions.
The Madhyama Agama includes two hundred twenty-two sūtras against one hundred fifty-two in the Pali Majjhima Nikāya. More than two-thirds of sutras appear in one compilation but not the other.
Enomoto Fumio published research on formation of original texts in Buddhist Study Reviews in 1986. Wang Jianwei and Jin Hui published their Collation and Annotation of Sañyuktāgama in 2014 at East China Normal University Press.