Sarah Corbett from a Facebook post, June 2016:

"I have some history on these mysterious beads! Made by one nomadic family in Mauritania called Lmalem . They travelled between Boutelamin, Kiffa and Nouakchott making these carved beads for the weddings of high status B'than Maure families. The family would supply the beads and have them carved. Originally done with Amber beads, but those would break, so since 1940 only French Amber ( Bakelite) was used. Name in Mauritania is Muhafen Luban. Meaning improved Amber. (source of the information is a Mauritanian friend from the region)."

I think that you have commented before that L'malem is the term used for silversmiths or metal (jewelry?) workers in general. The other interesting thing in Sarah's comment is that these beads possibly date only from the 1940s. This dating would indicate that PF beads reached Mauritania only since the onset of WWII - possibly in response to a disruption in the natural amber bead trade? Lots of unanswered questions.

One new development on my end is that it seems one of the carved beads I have may be natural amber, since it fluoresces under black light. I need to take apart the necklace and do more tests to be sure, since some plastics fluoresce.