I was one the developers responsible for implementing the netcode on Serious Sam. We often slept under the desks in the offices at croteam after lurking usenet. One post in particular described the QuakeWorld prediction system which inspired us. That night we coded a simplistic mvp as a colleague (hi dan) tested it over an old 486 nix machine acting as a router that we could simulate lag with. This was well before the actual game was built around it