I have spent too much time in Runneyeye trying to get a complete set of Blackened Alloy armour and this is the last piece. I have 2 other sets missing these as well. And The Blackened Iron sets (x4) missing the coif. Sounds feasible that the boots and possibly the coif met the same fate and were removed.
Now having said this my next drop will of course be the boots and/or coif.