Mandaeism
Before the printing press was invented, people copied texts by hand. The people doing this were called scribes. Each person's handwriting is special in certain ways. This was the same with scribes. A scribe might join two letters in a certain way, or he might do the dots on those letters that have them in a special way. Jorunn J. Buckley looked at these special marks the copyists left in the Left Ginza. That way he was able to show that the copying of that text goes back to the to the late 2nd or early 3rd century AD. These special marks show that the Mandaeans existed during the late Arsacid period at the very latest. A legend called  Harrān Gāwetā also strengthens this. According to this legend, the Mandaeans left Palestine after the destruction of Jerusalem in the 1st century AD and settled inside the Arsacid empire.  Although the Ginza continued to evolve under the rule of the Sassanians and the Islamic empires, few textual traditions can lay claim to such extensive continuity.