Some old knives with Delrin handles, or similar poly resin-based materials by other mfrs, had issues with the handles essentially bleeding off vapors or outgassing from the manufacturing process, and leaving a 'smoky' white deposit on the surface of the material. Some of Case's older black-handled Sod Busters have been known to have the problem. I think part of the issue, in those instances, was the knife being enclosed in plastic packaging that didn't allow the material to 'breathe' a bit, after manufacture. I think at least some of the old Case knives turned up with the problem after having remained in original packaging, in 'as new' condition, for a very long time (maybe years).
It's not the same sort of 'outgassing' that happens with old celluloid handles, which is bad news and very corrosive to any steel in proximity. But it leaves that whitish residue that doesn't come off easily, if at all. I don't know if there's an easy way to clean it up. I seem to recall some have managed to hide or disguise it somewhat, using oil, wax, Armor All or some type of treatment/coating applied to the surface.
Take a look at this old thread linked below, on the AAPK site. Read the post by '300Bucks' in that thread (he's a member/mod here on BF, too):
https://www.allaboutpocketknives.co...746&p=324042&hilit=White+handles+Buck#p324042
Edited to add:
Here's another link to an old thread here on BF, about the same (or similar) issue. In particular, take a look at post# 8 in that thread, from 'knarfeng' (also a mod here):
https://www.bladeforums.com/threads/scale-found-on-old-300-series-delrin.526265/
