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Selected and Standard is basically the same. If they have a stone that makes them suspect that the future owner might be slightly unhappy when he receives his stone, because e.g. the Coticule part is a bit thiner than average, or there is a glue line with uneven thickness, or the stone as a small void showing at one of the narrow side, or yet some other cosmetic issue, than they rate that Coticule "standard". In my book, it means: "don't come nagging about something that doesn't affect the hone's performance"...
Black manganese lines are more a quality marker than a cosmetic flaw (I personally love the way the looks of manganese lines and dots). As such that don't lead to a stone being graded "standard".