Dtm, I've spent a fair amount of time over the past 20+ years developing a set of charts that show Brit and Continental gun values (not to be confused with prices) as functions of Brand Value (BV), Original Quality (OQ), and Current Condition (CC). Several of the guys here have and use said charts with a very good level of expertise. While not "gospel," the charts have over the years shown a good correlation to auction results (a public knowledge of gun prices). The value of the charts is to jump-start learning. They require some expertise to use, but seem to provide a good return in speeding up the learning necessary to evaluate Brit and Continental guns.
Post back if you have further questions.
DDA
Rocketman;
Your data base of gun "values" interests me. Assuming these values (let's call them market values) are what individuals were inclined to pay for gun(s) during the data base collection period, is the data contained in an software application that could produce "curves" of the market value of the same gun(s) over the 20 year period?
