YC116 is when they were first detected. [ARC] Drifter Crisis history repository
Makoto Priano generally refers to them as meat puppets, and I concur. To me they appear to be corpses that have been ‘rewired’ with nanotech of some description and then used under some kind of remote or distributed control system.
The Drifter/Triglavian connection appears to hark back to the Tyrants of the Second Jovian Empire, that we really know very little about. The data we have managed to access so far, and pretty much from the new Triglavian message system, seems to indicate that the Triglavians were either a part of, or contemporary with that period and escaped to the Abyss around that time. Presumably because of the actions of the Tyrants, although the actual events are still unknown.
In my opinion its resource based, I see Drifters either scanning for, or harvesting resources. The one fear I have is that we will see improved Drifter vessels using mutaplasmid technology.