My impression is that by the time these books are printed and reach distribution channels they're already obsolete...the market has already changed. It's like newspapers...they're yesterday's news.
These guide books are simply a guide and nothing more. In a very volatile market like it was prior to the election they're only good for testing penetration of various calibers and loadings. Real world values change daily. The value guides are probably like used car Blue Book guides...they give the advantage to the dealer for what he'll give you for your trade-in but not for the selling price of his inventory...that goes by what the traffic will bear.
Of all the references out there I have found the "Gun Traders Guide" to be the least useful and totally inaccurate. I believe that, like RCA, someone bought the name and has been making money off of it. I could not and would not recommend this publication to anyone.
The Blue Book is the most useful because of more information as to grading. The Blue Book goes by the percentage of remaining original finish rather then the usual Good, Very Good, Excellent etc.
Also, the Blue Book has a good tutorial on HOW to grade a gun for value.
The Blue Book states that they arrive at the values based on what they observe the guns selling for at big gun shows.
As above, there's a long lead time between compiling the data, then getting it to the publisher and having it actually printed.
That means the values are always behind the curve.
The Gun Traders Guide is usually brought in play by a person buying a gun from an person who has no idea of the value.When selling the same gun the Blue Book is brought in play.The Gun Traders Guide has never had accurate values.