I can't speak for CMPA or QL, but I can speak a little bit on Unlagged:

- w/ Unlagged, the Server now stores a history buffer (g_activeSnapshots[]) of player states. When processing a action shot, it uses the timestamp sent by the client (cmd.serverTime) to interpolate or rewind states for collision checks (G_EvaluateTrajectory()). This allows the server rewinds player positions to the moment a client action occurred (eg: firing a shot)

- Unlagged reduces choppy movements by making clients use a snapshot buffer (cg.snap, cg.nextSnap) to interpolate positions with CG_InterpolateEntityPosition(). Extrapolation uses velocity vectors from the last known snapshot (currentState.pos.trDelta).

- Unlagged tries to compensate for high latency by rewinding entities to their positions at the time of the shot (ClientThink_real() and G_RewindEntities()). Uses a circular buffer (via lagometerSnapshot_t) to store past states.

- Position corrections (cg.predictedPlayerState) are interpolated over several frames using VectorLerp() to fix prediction mismatches between client and server.

- Commands are stored in a circular buffer (ucmds[]) and replayed when missing packets are detected (ClientThink_cmd()). This attempts to mitigate packet loss by buffering input commands for later execution