Yep - The Silvery Image is Opus I. The word "opus" refers to any musical composition and is usually divided in parts (ie. Father of Hate would be Opus I no. 2, but I guess there is some leeway). The number has to do with order of publication, not when it was composed. The Silvery Image was composed between 1998 and 2005, while The Alignment of Galaxies was August 2005, and The Origin of a Curse was January 2006.
Definitions of words are so ambiguous though.