Even if my wife and I get our meal fully comped because the kitchen messed up or it took a long time (has happened a few times, college town. We never complain or get upset, the managers just come over and apologize then comp it), we qt least tip as if it wasn’t comped, if we liked our server and/or the food a lot (both, most of the time) then we tip the full amount of the comped meal. Without fail the servers have been surprised that we tip at all when that happens