Hi OWF and Tunes; I have the 9th / 2005 edition of the Blue Book of Acoustic Guitars. Without commenting on its estimates of guitar values, it's missing some details in the Guild section and some of the details that are there aren't accurate. For example, it reports that certain models were available in certain colors when they weren't and vice versa; some reported as not available in certain colors when they were.
Maybe some of the inattention to detail can be laid off to the number of brands, models, and year-to-year changes, I don't really know. I think the Blue Book is a very useful reference for understanding who made what model guitars and when they made them but, having played and lost a few hands of 'Hans and The Blue Book', it isn't fully reliable in relation to Guild detail. I don't know enough about other makes to know whether that criticism applies elsewhere too.
John