>>714688347
I'm not too familiar with Lineage 2 situation as well, but far as I'm aware at some point dev builds were leaked and people were making custom shards ever since. Pretty sure you have to have same files as server expects you to in order to connect (they store all the data about items, mobs, etc, they're just giant tables or something like that).
Maybe, maybe not, I've played it a couple of times here and there in the past. Either way, L2 private servers are alive and well even to this day.