Shlama,
Regarding the Peshitta, page 87 says,
"In the Old Testament, this represents a direct translation from ancient Hebrew texts, probably done in Edessa or Arbela. The Peshitta remained the standard version for the Eastern churches, just as the Latin Vulgate did for the Western church."
On pages 88,89...
"Although they did not include them in the canon of scripture, all the Eastern churches knew many ancient Christian texts, including apocryphal Gospels and apocalypses, and many scholars quote from now-lost patristic texts and commentaries. One major influence for Syriac writers was the Diatessaron, which was widely used in Eastern churches before many bishops decided to abandon it on the grounds of Tatian's heretical leanings.
"Nevertheless, Syriac scholars continued to know and cite the work at least through the thirteenth century, giving them access to what might have been authentically ancient New Testament readings that were lost in later texts. Through the Diatessaron, for instance, scholars like Isho'dad and Bar Salibi knew the ancient story that at the moment of Christ's baptism, 'a great light shone' over the Jordan.
"Even at the end of the thirteenth century, 'Abdisho' bar Berikha not only knows the Diatessaron, but lists its as part of the canonical New Testament."
This last sentence reminds me of the quote from
The Nestorian Church: A Concise History of Nestorian Christianity in Asia from the Persian Schism to the Modern Assyrians (in
this thread):
"Ebedyeshu, metropolitan of Nisibis, gives: the Four Gospels, Acts, the Epistle of James, i Peter, i John, fourteen Epistles of Paul (inclusive of Hebrews). He also adds the Diatessaron of Tatian...reauthorization of the Diatessaron"
Shlama,