I saw some similar ones in Japan recently. I visited Tadatsuna, for example, and noticed a few old ones in the display room. I had a look at one, a yanagiba whose blade was sharpened down to about 1/2 of the original size (similar to the '15 year' photo above); wooden handle also had a dulled look. Mr Nagata said it was 20 years old and belonged to a chef, and so it had presumably been used on a daily basis for all that time, in which case you'd have to say it'd stood up well. Maybe there's a little tradition where chefs like this, when their prized knife has seen its day, return it to its maker when buying their new blade. I didn't ask if it was for sale, but guess it was kept there as a curio or to show how their knives would handle heavy use over time.
In other places I also saw lots of old blades being fixed up and/or rehandled. Some very rusted and neglected blades - home use, I would guess, and lots of santokus. With those in better condition, the kind whose owners maybe cared about them more and used them more frequently, the tangs would seem quite rusted out, in some cases to the extent that I'd wonder how strong they might be when re-handled. (Made me think about the advantages of welded-on stainless steel tangs, for sure.)