Essentially, the beads we think of as pumtek were made in the 1920s in Burma. They were made because of the following:

At that time, ancient beads (not doubt beads from India and Pyu/Mon copies of those beads) were being locally dug-up by people. They probably found a factory site, because a number of unfinished beads were recovered, and these were drilled to be worn. They became quite a fad. When the supply of old beads became more or less exhausted, they began to make their own versions of the old beads. Thus, pumtek beads were born.

Consequently, we should expect that occasionally an older bead is incorporated into a pumtek necklace—because these older beads were cherished and still circulating. Some will be broken because they have knocked-around for a long time.

I don' know that anyone can say whether Pyu/Mon beads date to any specific time, or have a recognized time range. I would have to reread some of the archaeological literature to be reminded what has been suggested. I just know these beads post-date the Indianization of the region, occurring about 2000 years ago + or -.

I hope this is an enticing bone.

Jamey