Other makers sold them as seconds, or broke them up for reuse as cullet, or just ignored the faults and sold them anyway. Quality control varies from place to place.
It may also have been someone else buying ZBS pieces to engrave onto. A master engraver who lived not far from me used to do this - he would buy in blanks from various places, so I see his work on handmade pieces made by Waterford Crystal and on machine made French and Italian, and even Chinese, glassware.
Welcome to the board too, Niya. 😀