I follow Old Timer knife prices, well not so much recently, but I can say that having the knife in it's original box can add significantly to the resale value. This is especially true with Old Timers due to the fact that most models were made in very large quantities and are therefore commonly available in the aftermarket. With dozens, or even hundreds, of 34OT (the most common model) knives available at any given moment, why would a serious collector settle for an incomplete example? And from the seller's aspect, what's to set one guy's 34OT apart from all of the others?
Let's say there's a dozen guys looking for a 108OT for their collections. And there are a dozen guys with a 108OT for sale. Of the dozen for sale four are new-in-box, four are unused but without their original packaging, and four are used. A likely scenario, the dozen guys will bid against each other for the knives in the best condition, which is obviously the N-I-B examples.
Now, a different example, say you have a knife that is very rare. The serious collectors will 'chase' it regardless of whether it has a box.
Even a third example: say you have a knife, even a semi-rare model, that no one cares about. The box won't really affect it's value either.
It's all about supply and demand.

And the answer to your question is, "It all depends."
Consider too that many knives are produced for years, sometimes decades, without even a tang stamp change. The original packaging is the only way to determine or even narrow the age of some knives.
One more thing I'd like to point out is that some collectors are specifically interested in vintage knife boxes. Some were very ornate, colorful, and detailed and help tell the story of a cutlery company and it's products. You sure won't find the company's full address or warranty information printed on the tang.

Some beautiful examples in this topic:
http://www.bladeforums.com/forums/s...ld-Pocket-Knife-Boxes?highlight=vintage+boxes