In the quest for accuracy:

I recant my proposition that plastic zi beads "were made at Lhasa." This was an incorrect memory on my part (!). What I was told was that two Tibetan brothers operated a factory in Nepal (probably at or near Kathmandu), where they have made plastic imitations of zi beads for decades. I figured out where I went wrong quite a while ago, probably before Gabrielle Liese passed away in 2011. But I did not take any opportunity to correct my mistake until now.

So this is it. JDA.