Weapons unaccounted for is not the same as HAVING WMDS.
It is an inconclusive statement it could mean the weapons still exist or could mean they do not exist and their disposal has not been properly accounted for.
In the address to the UN security council where he made this statement he also stated to the effect that no WMDs had been found or evidence to support that they did exist.
Nowhere did Blix to my knowledge draw the conclussion or state that it was his opinion based on some WMDs being unaccounted for that WMDs did exist in fact he stated or at least implied the very opposite.
