This is speculation on my part, based on the idea that the Europeans were noted for making beads for the Africans based on what the Africans already were using for their adornments:

The first disks were made by the Africans out of palm nut or other nut, shell, or wood. We know that disk beads made from ostrich shell were common, so thin disk beads were desirable.

I further speculate that the Europeans introduced dIsk beads from vulcanite sheet stock, then Celluloid, and finally from vinyl. I have documentation that the Celluloid beads were replaced as soon as possible due to the high flammability of the Celluloid disk, which caused severe burns to people and also fires aboard the merchant ships. So perhaps the vinyl versions were in play prior to WWII - needs more research.

I believe that some palm nut disks can be well over 100 years old. I imagine that they were saved and incorporated into updated strands when the Celluloid disks became available. Of course, it also appears that the palm nut disks are still being made. A lot of pure strands of palm or coconut disks appear to have little to no wear, in contrast to the very smooth edges of the old ones.