First, I think these beads are not as old as expressed.

Agate beads have been sold out of Nepal for over a decade, that were actually made in India. These are often said be "Tibetan," when they are actually only something like Tibetan-style beads. Or, as I like to say, "made for the Tibetan market." They are not authentic-looking—probably because the manufacturers in India are not exploiting the same carnelian or agate as originally used (that came from Yunnan in the instance of Tibetan carnelian, called pema raka).

About thirty years ago, the Chinese made reproductions of pema raka beads, apparently from the same Yunnan sources. But these beads are distinctive. In more-recent years, Chinese manufacturers have also made beads for the Tibetan market.

I would guess your beads are either Indian or Chinese, and are more recent than you may suppose.

Jamey