Are you cataloging variations in the size of inserts? I think the two chips below were made at different times, not only because of the inserts, but because the blue clay used to make the chip on the right seems to have more of the little sparkly things (lead?) than the one on the left.

Not that it's a variation, but the chip on the right also has an indentation at the edge of the "A" at the 7 o'clock position. It's hard to see in the photo, but it is about the size of a BB and in fact looks as though someone shot the chip with a BB gun. I suppose it happened when the clay was soft, but then again I don't know much about the process of making chips.