For a used current-production gun, like say a used S&W 686, sure, the numbers might mean something.
But for a discontinued gun? What's a recent Winchester 94 "worth", for example? Some of the low-end versions are near-junk quality, for a Winchester. But they're worth whatever people are willing to pay, today.
As a used gun? Some recent low-end 94s are "skip it" items as guns. But as a "collectible", they can go for a lot more than they're worth as a hunting rifle. Maybe in a few years, that will all level out, and the good ones (by year or model) will go for a lot more than the recent low-end versions. But right now, the prices are kinda silly for some of them.
Now, consider other rare variants of guns. I recently bought a Marlin 39M Octagon. Now the 39M is a much-loved variant of a gun that has a veritable cult following. However, most examples have round barrels. There are some commemorative versions with octagon barrels, but AFAIK Marlin only made about 2000 like mine, not commemoratives, with Microgroove rifling.
A decent 39M with the regular barrel runs around $300, if you can find one for sale, which is hit or miss. $300 is high enough for an old .22. The only Octagon I could find reference to sold recently for $500 on the auction sites. I paid $400.
Did I get a
collectible rifle for $100 under market, or did I pay $100 too much for a
used rifle with a neat-o feature that adds nothing to it in actual utility?
What IS the market? Very few of these exact rifles exist, and fewer change hands. What will the next one go for? $200? $600? Who knows? The Blue Book doesn't know, either.