I am not sure if Szeth's blade is indeed a honorblade. His blade is described as "long and thin, edged on both sides, smaller than most others". Also the chapter icons show a blade that is simple and not as honorblades are described - honorblades are described as "Each was a masterly work of art, flowing in design, inscribed with glyphs and patterns."
I am not sure if that icon was deliberately pictured wrong to mislead but I doubt it. Also I seem to recall that the honorblades were long (longer than shardblades) but I cant seem to find any quotes for it. I am not confided that I recall that information accurately though. I would appreciate it if you can point me to source of information as to why you think that Szeth's blade is an honorblade.