A lot of the value of a knife - up to 60% - depreciates if the buyer thinks the knife may have been used. Proving otherwise is up to the seller and his presentation of authenticity - which goes beyond the physical evidence of the knife and box.
Popular knives in current product, even NIB, seem to depreciate because of the quantity available on the market. And it never helps to discover the price you might be asking is undercut by an internet retailer, even though their reputation is poor. It's still considered a potential low price despite a six month wait.
Of course, the most decisive issue is that you actually have to be trying to sell the knife in question. Then the issues of the day become important. Right now, I doubt some have the disposable income to keep demand up for certain knives, and prices may be flat or depressed. Public demand - popularity - also affect pricing. Tacticool knife prices are supported by demand among survivalists, but art knives may be in the cooler. A year from now, it could be the opposite due to other factors, or the loss of another maker could send their remaining pieces to high prices. It's happening with some Camillus products.
In a serious downturn, or even worse, the knife finally gets valued for what utility it has, artwork and makers name be damned. At that point, a common carbon steel kitchen knife is considered the base line, and it takes a lot of knowledge to appreciate any unseen advantages in materials or construction. In fact, a trip to the local DAV/Goodwill/Salvation Army thrift store can quickly show that - carbon steel kitchen knives rarely surface. It's mostly dull stainless cheapware. The average family member won't let the others go precisely because of the utility value, regardless of rusting.
Knives do depreciate, many just the same as an automobile driven off the showroom floor. You can put it on blocks in a sealed nitrogen filled room and wait decades for appreciation. Some never do - I haven't seen too many mint '76 Mustangs on ebay. Enjoy a collection for what you think it is, but as far as using financial descriptives, don't bother. 99% of all knives are considered an expense, and treated as durables subject to pilfering. Those are the terms the Army uses, and I think most apt.