Agreed about the weaver and the pattern from that weaver. The problem comes when you are trying to match from a weaver you don't know (e.g., my 25 year old kilt), or a weaver who no longer makes that pattern (e.g. my MoD Forbes from Robert Noble). You can come close, and people might not notice if you are at a formal setting with lower light (e.g., that Burns night supper).