The Georgian church lost its autocephaly to the Russian Empire in 1811, and over the century that followed the imperial administration pressed Georgian parishes toward Russian four part harmony and Church Slavonic. The chant that had been carried by ear in the monastic schools was, quite suddenly, at risk of simply not being passed on.
The response was a transcription campaign. From the 1880s a group of chanters and clergy, among them the Karbelashvili brothers and the singer Pilimon Koridze, sat with the surviving masters of both the eastern and western schools and wrote what they sang into Western staff notation. Several thousand chants were recorded that way over roughly three decades. The work was not neutral: staff notation cannot hold the intonation of the western school exactly, and the transcribers made choices that the modern repertory has inherited. But without it there would be very little left, because the Soviet period closed the schools that had produced the singers.
Revival followed the end of Soviet rule. Chant is taught again in dedicated schools, the manuscript transcriptions have been catalogued and published, and ensembles sing the western repertory that had come closest to disappearing. What is sung today is therefore a living tradition reconstituted from a written record of itself, which is a different thing from an unbroken oral chain, and Georgian chant scholarship is unusually candid about the difference.