Can't exactly answer your question...though all I can assume after seeing many, many of the same "chips" in collections thru the years with MOST being in their original state of preservation, is that the ones which differ from the majority are probably not maintained in a way as the well-preserved chips are. Meaning; there are a lot of factors such as humidity, heat, sunlight; artificial lighting, chemical reactions with contact of certain plastics, peper; cleaning products such as soap,
oils or abrasives and the cloth used... or whatever used in storing under varied conditions...

When I use the term "chips" I'm referring to all types of manufacture; plastic, clay composition or whatever else.

In short; there is a reason why some chips that were made exactly in the same production; as long as 70 or 80 years ago are no different than the day they were made... and some from that same production are ready for the trash bin.