Not that it pertains to these beads, nor many glass beads in particular, but other beads made from soft materials have off-round perforations due to string abrasion. And even harder materials (if worn over a long time) can share this feature.

Old amber beads from certain kinds of necklaces develop both tear-shaped and "key-hole" or slotted perforations. About thirty years ago, Peter Francis and I had some dialogue about this in The Bead Journal. He maintained the beads were drilled this way on purpose, "'to make them hang correctly in a circle.' My reply essentially said that the wedge shape of the beads made them tend to form a close-together ring; but that if they were loose enough to turn (spin or rotate), or were forced toward the thin edge and abraded (depending on where in the necklace the beads were situated)—and that these actions altered the shapes of the perforations.

I am confident I am correct. As a career bead-stringer, I had and have rather more practical experience with these issues than did Peter.

Any drilled bead that is poorly worked, in a certain way, could conceivably have an eccentric perforation. Imagine, the driller began the perforation, stopped, and began again adjacent to the first false-start. The aperture would not be circular. Any number of scenarios may be possible.

Jamey